Sharif Digital Repository

Nowadays, cervical disorders are common due to human lifestyles. Accordingly, the cage design should be optimized as an essential issue. For an optimal design, an objective function is utilized to calculate the proper geometrical parameters. Additionally, the base material of the cage plays a key role in its functionality and final cost. Novel materials are currently introduced with more compatibility with the bone in terms of mechanical and chemical properties. In this study, a cervical cage was modeled based on PEEK material with three types of tooth designs on its surface. The cervical cage is assumed to be implanted between C6 and C7 vertebrae. The geometric parameters of the cage were... 

Droplet microfluidics is a platform of microfluidics in which two immiscible fluids are used to generate droplets for various biomedical applications. This platform introduces several advantages in applications such as cell lysis, cell culture, co-culture, and cell encapsulation. The most important issues regarding droplet generation devices are the fabrication complexity and maintenance of these devices. In this study, a simple and easy-to-fabricate microdroplet generator is designed and fabricated to resolve these issues. Furthermore, since this device is easy to fabricate and use, it can play a key role in the fabrication of medical devices for controlling infectious diseases in poor and... 

The present study aims to challenge the existing finite element models in terms of one of the most important practical parameters, i.e. coverage. Important models from the literature are re-simulated and their resulted treated surfaces are carefully examined. Result of this study shows that existing finite element models could not reflect the realistic coverage. A variable dimension symmetry cell is developed in order to acquire full coverage and at the same time not increasing the computational cost. This model can successfully simulate the surface nanocrystallization by severe shot peening in which the amount of coverage is much higher than conventional shot peening  

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field’s characteristics... 

Cell lysis is an essential primary step in cell assays. In the process of cell lysis, the cell membrane is destroyed and the substances inside the cell are extracted. By utilizing a droplet-based microfluidic platform for cell lysis, the mixer unit that is required for mixing lysis reagents with the cells can be excluded, and thus, the complexity of the fabrication process is reduced. In addition, lysing the cells within the droplets will prevent the cells from exposure to the channel walls, and as a result, cleanliness of the samples and the device is maintained. In this study, cell lysis within the droplets and the parameters affecting the efficiency of this process are investigated using... 

The beneficial effects of shot peening on fatigue life of mechanical components are well known. However, there are some reports in the literature that indicate inappropriate shot peening parameters tend to reduce the fatigue life. It is therefore, the purpose of this study to find a logical quantitative justification for these observations. Using finite element method, a dynamic elasticplastic simulation of shot peening was presented. Effect of shot velocity and size on surface morphology after shot peening were examined. Fatigue crack initiation life calculation of shot peened specimens revealed that beneficial effect of shot peening significantly vanishes in the case of high velocities and... 

Separation and lysis of RBCs play an important role in diagnosis of different diseases. Although they have been partially studied in several researches, a comprehensive study on integrating both separation and lysis units on a single chip has been seen rarely in the literature. Also, the factors related to the chemical lysis process have not been investigated in detail. In this study, we introduce a novel microfluidic channel design for sequential RBC's separation and lysis. For the separation part, an active method with an electric field was applied to the cells. Besides, a novel mixer was designed for mixing the cell solution and lysis reagent. In the lysis section, we used a mathematical... 

Coverage is one of the most important parameters which is always used in practice to characterize a shot peening process. At the same time however, it is the most missing parameter in the finite element simulations of this process. This study aims to relate shot peening simulation to the actual coverage that is developed during the process. Accordingly, two important models from literature are re-simulated and their capability to predict an actual coverage is assessed. Results of this study illustrate that full coverage situation is not captured by these models. Thereafter, a random finite element simulation along with a step by step examination of the treated surface is adopted in order to... 

Cancer diagnosis has recently been at the forefront of recent medical research, with ongoing efforts to develop devices and technologies for detecting cancer in patients. One promising approach for cancer diagnosis is the detection of Circulating Tumor Cells (CTCs) in blood samples. Separating these rare cells from the diverse background of blood cells and analyzing them can provide valuable insights into the disease's stage and lethality. Here we present the design and fabrication of a centrifugal microfluidic platform on a polymeric disk that utilizes centrifugal forces for cell isolation. The separation units exploit both active and passive methods. In other words, in addition to... 

Application of the colloidal gas aphrons (CGAs) in minimizing formation damage by plugging pore mechanism is now wildly accepted due to numerous successful field experience. One of the pivotal factors which affects the pore blockage ability of micro-bubbles is their stability. This experimental study tries to investigate the possible synergistic effect of nanoparticles on improving the stability and other properties of non-aqueous CGA drilling fluids, in both bulk and porous media. In particular, two types of hydrophobic nanoparticles including silicon dioxide nanopowder coated with 2 wt% Silane and nanoclay, in presence of a treated version of bentonite (Bentone 34) as a stabilizer and... 

Recent developments in the space industry and the great tendency to define efficient, precise and low cost missions are the main reasons for the growing interest in satellites formation flight. Regarding the aforementioned, the study of multiple satellites control methods is the subject of the present paper. In this paper, two linear robust control strategies are applied to position control system of certain satellites in the virtual structure formation flight. The proposed controllers are designed considering different parametric uncertainties such as semimajor axis and eccentricity changes as well as some disturbances like second term of gravitational acceleration function (j2) and drag... 

In this paper, a new multi-secret threshold scheme based on linear algebra and matrices is proposed. Unlike many recently proposed methods, this method lets the use of conventional cryptographic algorithms in sharing multiple secrets. Our scheme is a multi-use scheme, which in some cases, the amount of computations is considerably reduced. Also, in this paper bounds on the maximum number of participants, for a given threshold value, are obtained. © 2010  

Shot peening is one of the most effective surface treatments for improving the fatigue strength of machine elements. In this paper, a new finite element-based model to predict the effect of coverage on the surface state is proposed and critically discussed. By this model, the effects of Rayleigh damping, mesh size, and target dimensions on residual stress profile are investigated using a random impingement simulation of shot peening. Moreover, the model enables the realistic simulation of shot peening process with an affordable computational time with respect of present approaches without reducing the number of impacts and analysis accuracy: the computational time was reduced by 25% in... 

Background: A speller system enables disabled people, specifically those with spinal cord injuries, to visually select and spell characters. A problem of primary speller systems is that they are gaze shift dependent. To overcome this problem, a single Rapid Serial Visual Presentation (RSVP) paradigm was initially introduced in which characters are displayed one-by-one at the center of a screen. New method: Two new protocols, Dual and Triple shifted RSVP paradigms, are introduced and compared against the single paradigm. In the Dual and Triple paradigms, two and three characters are displayed at the center of the screen simultaneously, holding the advantage of displaying the target character... 

Non-Convex Economic Dispatch (NED) has been addressed as an open and demanding optimization problem in power systems. Due to the fact that realistic ED problems have non-convex cost functions with equality and inequality constraints, conventional search methods are unable to effectively find the global solution. In recent years, because of their great potential to achieve optimal or close-to-optimal solution, meta-heuristic optimization techniques have attracted significant attention to tackle the complexity of NED problems. In this paper, an efficient approach is proposed based on Imperialist Competitive Algorithm (ICA). The proposed algorithm named multi-operator ICA (MuICA) merges the... 

Nerve repositioning surgery is one of the treatments chosen for the patients with edentulous posterior atrophic mandible. Like any other treatments, this therapy has its advantages and disadvantages, indications and contraindications. The most important complication of this procedure is neurosensory disturbance. This problem may occur at different stages of the treatment. One common time when nerve damage happens is when the nerve is located outside the canal and drilling and insertion of the implant are performed. Accordingly, this report describes a simple and feasible method to retract and protect nerves outside the canal during the treatment of nerve transposition. This will reduce the... 

Nerve repositioning surgery is one of the treatments chosen for the patients with edentulous posterior atrophic mandible. Like any other treatments, this therapy has its advantages and disadvantages, indications and contraindications. The most important complication of this procedure is neurosensory disturbance. This problem may occur at different stages of the treatment. One common time when nerve damage happens is when the nerve is located outside the canal and drilling and insertion of the implant are performed. Accordingly, this report describes a simple and feasible method to retract and protect nerves outside the canal during the treatment of nerve transposition. This will reduce the... 

Rock formations are always under in situ stresses due to overburden or tectonic stresses. Drilling a well will lead to stress redistribution around the well. Understanding such a stress redistribution, and adopting a proper failure criterion, play a vital role in predicting any potential wellbore failure. However, most of the published analytical models are based on assumptions that do not satisfy the boundary conditions during production, that is, when the well pressure is less than the pore pressure. This paper is aimed at the modeling of the stress regime around the wellbore through combining the poroelastic model with proper boundary conditions under different flow regimes. As a result,...