Sharif Digital Repository

Sweeping gas membrane distillation process was studied using flat sheet hydrophobic PTFE membrane. The effects of operating parameters, including feed temperature, feed flow rate, sweeping gas flow rate, and feed concentration on the permeate flux, were determined. The feed temperature significantly influenced the permeate flux. Increasing the feed temperature increased the permeate flux. The increase of feed concentration caused to reduce the permeate flux due to the increase of concentration polarization effect and reduction of vapor pressure difference. Sweeping gas flow rate led to increase the permeate flux due to reduction of vapor pressure in the permeate side. Higher air flow rate... 

In this work, desalination of saline brines using the sweeping gas membrane distillation (SGMD) process is investigated. The Taguchi method was applied for optimization of the operating parameters. An L9 orthogonal array was used to investigate the influence of pertinent variables, including feed temperature (Tf: 45°C, 55°C and 65°C), feed flow rate (Qf: 200, 400 and 600 mL/min), feed concentration (Cf: 10, 25 and 50 g/L) and sweeping gas flow rate (Qc: 4, 10, and 16 SCFH) on the distillate flux. Results of the experiments showed that maximum distillate flux, which was about 10 L/m2 h, obtained at 65°C feed temperature, 16 SCFH sweeping gas flow rate and brackish water with 10 g/L salt... 

As membrane distillation (MD) is an under-developed separation process, specific membranes for MD applications are not yet commercially available. Therefore, microporous polymeric membranes made of hydrophobic materials fabricated for microfiltration purposes are usually used for MD applications. Characterization of such kind of membranes is important in order to achieve a better in-depth understanding of their performance and to fabricate specific membranes for MD process. One of the emerging characterization methods is atomic force microscopy (AFM) analysis. AFM is a newly developed high-resolution method that is useful for studying the surface topography of various types of membranes, and... 

The 1991 NIOSH Lifting Equation (NLE) is widely used to assess the risk of injury to spine by providing estimates of the recommended weight limit (RWL) in hands. The present study uses the predictive equations developed based on a detailed trunk musculoskeletal biomechanical model to verify whether the RWL generates L5-S1 loads within the limits (e.g., 3400N for compression recommended by NIOSH and 1000N for shear recommended in some studies). Fifty lifting activities are simulated here to evaluate the RWL by the NLE and the L5-S1 loads by the predictive equations. In lifting activities involving moderate to large forward trunk flexion, the estimated RWL generates L5-S1 spine loads exceeding... 

In this work, sweeping gas membrane distillation (SGMD) process was used for concentrating of glucose syrup. The main questions in this work include: is SGMD process practical for concentrating of glucose solution prior the fermentation step in bioethanol process?. and are the commercially available hydrophobic membranes sufficient enough to develop the SGMD process in pilot scale for this issue?. To answer these questions, SGMD process was performed using three commercial membranes made of PP, PVDF and PTFE. All membranes characterized using scanning electron and atomic force microscopes for their morphological and topographical features. Important operating parameters including feed... 

In this work, two-membrane distillation (MD) modes, direct contact MD, and sweeping gas MD were investigated for synthesized and real (Persian Gulf) seawater desalination. A commercial PTFE membrane with 0.22 μm pore size was characterized (using atomic force microscopy and scanning electron microscopy) and was used for experiments. A multipurpose plate and frame MD module was used for desalination experiments. The effects of various operating conditions and MD module design, as well as feed type on the permeation flux have been studied. The feed temperature was found to be the most effective operating parameter. The flow rate in both sides of the MD module was found to be effective;... 

In this study the effects of using different musculoskeletal models on load-displacement behavior of FE models of the human lumbar spine under external loads and moments have been analyzed in terms of equilibrium and clinical stability. A simplified and a complex architecture of muscles have been integrated to FE based models of lumbar spine and were loaded to simulate the load carrying behavior of human lumbar spine in flexion, extension and lateral bending. The displacement values as well as muscle forces have been computed and compared in both cases using optimization methods with different cost functions. The models showed similar kinematics in pure flexion but the simplified model... 

In this paper, particle swarm optimization (PSO) is applied to synchronize chaotic systems in presence of parameter uncertainties and measurement noise. Particle swarm optimization is an evolutionary algorithm which is introduced by Kennedy and Eberhart. This algorithm is inspired by birds flocking. Optimization algorithms can be applied to control by defining an appropriate cost function that guarantees stability of system. In presence of environment noise and parameter uncertainty, robustness plays a crucial role in succeed of controller. Since PSO needs only rudimentary information about the system, it can be a suitable algorithm for this case. Simulation results confirm that the proposed... 

Spine musculoskeletal (MS) models make simplifying assumptions on the intervertebral joint degrees-of-freedom (rotational and/or translational), representation (spherical or beam-like joints), and properties (linear or nonlinear). They also generally neglect the realistic structure of the joints with disc nuclei/annuli, facets, and ligaments. We aim to develop a novel MS model where trunk muscles are incorporated into a detailed finite element (FE) model of the ligamentous T12-S1 spine thus constructing a gold standard coupled MS-FE model. Model predictions are compared under some tasks with those of our earlier spherical joints, beam joints, and hybrid (uncoupled) MS-FE models. The coupled... 

The purpose of this study was the production of copolymers and terpolymers with highly hydrophilic–hydrophobic properties, using inexpensive and available monomers as potential enhancing oil recovery (EOR) and water production control agents for high-temperature and high-salinity (HTHS) oil reservoirs. For this purpose, several copolymers and terpolymers with different molar percentage of acrylamide/styrene, acrylamide/maleic anhydride, and acrylamide/styrene/maleic anhydride were synthesized by the inverse emulsion polymerization technique. The presence of hydrophobic styrene and hydrophilic maleic anhydride monomers in the copolymer and terpolymer structure, provided some unique properties... 

Using the cross-correlation of the wavelet transformation, we propose a general method of studying the scale dependence of the direction of coupling for coupled time series. The method is first demonstrated by applying it to coupled van der Pol forced oscillators and coupled nonlinear stochastic equations. We then apply the method to the analysis of the log-return time series of the stock values of the IBM and General Electric (GE) companies. Our analysis indicates that, on average, IBM stocks react earlier to possible common sector price movements than those of GE  

In this paper, the tip tracking control problem of a Timoshenko micro-cantilever beam is investigated. The beam is actuated by a piezoelectric layer laminated on one side of the beam. Dynamic equations of the beam and piezoelectric layer are found using the Hamilton principle. By employing the Galerkin projection method, state space representation of the system is derived. Then, a cascade control loop is used for tracking control of the beam's tip. The cascade control structure consists of an inner loop stabilizer and an outer loop proportional-integral-derivative controller. The stabilizer has a linear feedback form whose states are obtained through a linear observer which is based on the... 

Background The ratio of total lumbar rotation over pelvic rotation (lumbopelvic rhythm) during trunk sagittal movement is essential to evaluate spinal loads and discriminate between low back pain and asymptomatic population. Methods Angular rotations of the pelvis and lumbar spine as well as their sagittal rhythm during forward flexion and backward extension in upright standing of eight asymptomatic males are measured using an inertial tracking device. The effect of variations in the lumbopelvic ratio during trunk flexion on spinal loads is quantified using a detailed musculoskeletal model. Findings The mean of peak voluntary flexion rotations of the thorax, pelvis, and lumbar was 121 (SD... 

In this paper, the tip tracking control problem of a Timoshenko micro-cantilever beam is investigated. The beam is actuated by a piezoelectric layer laminated on one side of the beam. Dynamic equations of the beam and piezoelectric layer are found using the Hamilton principle. By employing the Galerkin projection method, state space representation of the system is derived. Then, a cascade control loop is used for tracking control of the beam's tip. The cascade control structure consists of an inner loop stabilizer and an outer loop proportional-integral-derivative controller. The stabilizer has a linear feedback form whose states are obtained through a linear observer which is based on the... 

Two artificial neural networks (ANNs) are constructed, trained, and tested to map inputs of a complex trunk finite element (FE) model to its outputs for spinal loads and muscle forces. Five input variables (thorax flexion angle, load magnitude, its anterior and lateral positions, load handling technique, i.e., one- or two-handed static lifting) and four model outputs (L4-L5 and L5-S1 disc compression and anterior-posterior shear forces) for spinal loads and 76 model outputs (forces in individual trunk muscles) are considered. Moreover, full quadratic regression equations mapping input-outputs of the model developed here for muscle forces and previously for spine loads are used to compare the... 

Background: Asymmetric lifting activities are associated with low back pain. Methods: A finite element biomechanical model is used to estimate spinal loads during one- and two-handed asymmetric static lifting activities. Model input variables are thorax flexion angle, load magnitude as well as load sagittal and lateral positions while response variables are L4-L5 and L5-S1 disc compression and shear forces. A number of levels are considered for each input variable and all their possible combinations are introduced into the model. Robust yet user-friendly predictive equations that relate model responses to its inputs are established. Findings: Predictive equations with adequate... 

Response surface methodology is used to establish robust and user-friendly predictive equations that relate responses of a complex detailed trunk finite element biomechanical model to its input variables during sagittal symmetric static lifting activities. Four input variables (thorax flexion angle, lumbar/pelvis ratio, load magnitude, and load position) and four model responses (L4-L5 and L5-S1 disc compression and anterior-posterior shear forces) are considered. Full factorial design of experiments accounting for all combinations of input levels is employed. Quadratic predictive equations for the spinal loads at the L4-S1 disc mid-heights are obtained by regression analysis with adequate... 

We investigated the effect of loading rate on tensile properties of sheep bone-anulus-bone specimens in axial direction. Disc anulus Samples with adjacent bone attachments were prepared from lateral, posterior and anterior regions of sheep lumbar spinal segments. The specimens were then tested at different strain rates under non-destructive cyclic tensile loading followed by destructive tensile loading. Each specimen was prepared by embedding the bony parts in the polymethylmetacrylate (PMMA) exposing the anulus portion to support tension. The results of non-destructive cyclic tests indicated a decrease in the hysteresis energy loss as strain rate increased. In the destructive tests, no... 

Trunk muscle forces and internal loads are computed under simulated standing postures while carrying a load using a nonlinear finite element model of the T1-S1 spine with realistic nonlinear load-displacement properties. A novel kinematics-based algorithm is applied that exploits a set of a priori known spinal sagittal rotations to solve the redundant active-passive system. The loads consist of upper body gravity distributed along the spine plus 200 N held in hands either in front or on sides. Predictions are in good agreement with reported measurements of posture, muscle EMG and intradiscal pressure. Minimal changes in posture (posterior pelvic tilt and lumbar flattening) substantially...