Characterization of the effect of joint clearance on the energy loss of flexible multibody systems with variable kinematic structure

Ebrahimi, Saeed,Salahshoor, Esmaeil,Moradi, Shapour Techno-Press 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5

Clearances are essential for the assemblage of mechanisms to allow the relative motion between the joined bodies. This clearance exists due to machining tolerances, wear, material deformations, and imperfections, and it can worsen the mechanism performance when the precision and smoothly-working are intended. Energy is a subject which is less paid attention in the area of clearance. The effect of the clearance on the energy of a flexible slider-crank mechanism is investigated in this paper. A clearance exists in the joint between the slider and the coupler. The contact force model is based on the Lankarani and Nikravesh model and the friction force is calculated using the modified Coulomb's friction law. The hysteresis damping which has been included in the contact force model dissipates energy in clearance joints. The other source for the energy loss is the friction between the journal and the bearing. Initial configuration and crank angular velocity are changed to see their effects on the energy of the system. Energy diagrams are plotted for different coefficients of friction to see its influence. Finally, considering the coupler as a flexible body, the effect of flexibility on the energy of the system is investigated.

Characterization of the effect of joint clearance on the energy loss of flexible multibody systems with variable kinematic structure

Saeed Ebrahimi,Esmaeil Salahshoor,Shapour Moradi 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5

Clearances are essential for the assemblage of mechanisms to allow the relative motion between the joined bodies. This clearance exists due to machining tolerances, wear, material deformations, and imperfections, and it can worsen the mechanism performance when the precision and smoothly-working are intended. Energy is a subject which is less paid attention in the area of clearance. The effect of the clearance on the energy of a flexible slider-crank mechanism is investigated in this paper. A clearance exists in the joint between the slider and the coupler. The contact force model is based on the Lankarani and Nikravesh model and the friction force is calculated using the modified Coulomb\'s friction law. The hysteresis damping which has been included in the contact force model dissipates energy in clearance joints. The other source for the energy loss is the friction between the journal and the bearing. Initial configuration and crank angular velocity are changed to see their effects on the energy of the system. Energy diagrams are plotted for different coefficients of friction to see its influence. Finally, considering the coupler as a flexible body, the effect of flexibility on the energy of the system is investigated.

Photo-Assisted Sondegradation of Hydrogels in the Presence of TiO₂ Nanoparticles

Ebrahimi, Rajabali,Tarhandeh, Giti,Rafiey, Saeed,Narjabadi, Mahsa,Khani, Hamed Korean Chemical Society 2012 대한화학회지 Vol.56 No.1

The degradation of one of the commercially important hydrogel based on acrylic acid and acryl amide, (acrylic acid-co-acryl amide) hydrogels, by means of ultrasound irradiation and its combination with heterogeneous ($TiO_2$) was investigated. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. The extent of sonolytic degradation increased with increasing ultrasound power (in the range 30-80 W). $TiO_2$ sonophotocatalysis led to complete (acrylic acid-co-acryl amide) hydrogels degradation with increasing catalyst loading, while, the presence of $TiO_2$ in the dark generally had little effect on degradation. Therefore, emphasis was totally on the sonolytic and sonophotocatalytic degradation of hydrogels and a synergy effect was calculated for combined degradation procedures (Ultrasound and Ultraviolet) in the presence of $TiO_2$ nanoparticles. $TiO_2$ sonophotocatalysis was always faster than the respective individual processes due to the enhanced formation of reactive radicals as well as the possible ultrasound-induced increase of the active surface area of the catalyst. A kinetics model based on viscosity data was used for estimation of degradation rate constants at different conditions and a negative order for the dependence of the reaction rate on total molar concentration of (acrylic acid-co-acryl amide) hydrogels solution within the degradation process was suggested.

A RESURF LDMOSFET with a Dummy Gate on Partial SOI

Behzad Ebrahimi,Behrouz Afzal,Ali Afzali-Kusha,Saeed Mohammadi 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.5

In this paper, we propose a laterally double-diffused metal-oxide-semiconductor field-effect transistor (LDMOSFET) that uses a dummy gate on top of the lightly-doped drain (LDD) region in a reduced surface field (RESURF) structure. The structure is based on the partial silicon-on-insulator (PSOI) structure to increase the operating frequency of the device. The use of the dummy gate induces another electric field peak in the structure, which increases the breakdown voltage of the transistor. It also improves the gate-drain feedback capacitance, the transconductance, and the ON-resistance of the device. For a LDD length of 3 µm, the breakdown voltage increases about 10%, the transconductance increases over 200%, and the ON-resistance decreases about 45%. When a LDD length of 10 µm is used, the increase in the breakdown voltage is 17%. In addition, we propose a breakdown voltage model for the structure, which may be used to optimize the design of the structure.

Dexterity characterization of the RPR parallel manipulator based on the local and global condition indices

Vahid Rezania,Saeed Ebrahimi 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

In this paper, the kinematic performance of a planar parallel manipulator 3-RPR is investigated. Based on the constraint equations, robot geometric Jacobian matrix is calculated. Since the end-effector of the 3-RPR planar parallel manipulator performs both translational and rotational motions, robot geometric Jacobian matrix is transformed to a homogeneous form. This method defines a new Jacobian that transforms the linear velocities of two points on the end-effector to the actuator velocities. The velocity manipulability index is used for studying the ability of the manipulator to move. The manipulator distance singularity and kinematic accuracy is checked out by using the Local conditioning index (LCI) and Global conditioning index (GCI). The effect of Jacobian matrix homogenization on both the LCI and manipulability index is investigated in detail. Furthermore, the relation between LCI and the manipulability ellipsoids for certain moving platform orientations is studied. The paper is finally concluded by checking out the shapes of the manipulability ellipsoids for different moving platform orientations over the whole workspace.

Evaluation of Factors Impacting Cosmetic Outcome of Breast Conservative Surgery - a Study in Iran

Olfatbakhsh, Asiie,Mehrdad, Neda,Ebrahimi, Mandana,Alavi, Nasrin,Hashemi, Esmat,Kaviani, Ahmad,Najafi, Masoume,Haghighat, Shahpar,Arefanian, Saeed Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.6

Background: Breast conservative surgery (BCS) followed by radiotherapy is the standard approach in management of stage I-II breast cancer. Several factors can affect cosmetic outcomes. The aim of this study was to evaluate the cosmetic results of BCS and influencing factors in the Iranian Breast Cancer Research Center. Materials and Methods: Patients who had undergone BCS were included. Photographs were taken of both breasts of the patients in three aspects and were evaluated by three specialists. The cosmetic scores were calculated based on a standard questionnaire. The data were analyzed using univariate and multivariate regression for relationships between cosmetic scores and clinical data. Results: A total number of 103 patients were included in the study. Mean age and BMI of the patients were $46.8{\pm}8.9$ and $28.1{\pm}3.9$, respectively. Breast cup sizes C and D accounted for 74.7% of the study group. The mean cosmetic score obtained from three referees was 5.72+2.06, consisting of 35.9% excellent-good, 35% moderate, and 29.1% unsatisfactory results. Patient BMI, volume of the resected tissue and breast cup size (D) showed significant correlation with the cosmetic score. On multivariate regression analysis, cosmetic score and BMI (p=0.022,) as well as breast cup size (p=0.040), remained significant. Conclusions: Immediate or delayed symmetrization of the breasts is suggested during breast conservative surgery, meanwhile performing oncoplastic techniques to improve the results significantly. Also it is suggested to discuss anticipation of less satisfactory results with patients having higher BMI and large breast cup size.

Energy absorption characteristics of diamond core columns under axial crushing loads

Nader Vahdat Azad,Saeed Ebrahimi 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.3

The energy absorption characteristics of diamond core sandwich cylindrical columns under axial crushing process depend greatly on the amount of material which participates in the plastic deformation. Both the single-objective and multi-objective optimizations are performed for columns under axial crushing load with core thickness and helix pitch of the honeycomb core as design variables. Models are optimized by multi-objective particle swarm optimization (MOPSO) algorithm to achieve maximum specific energy absorption (SEA) capacity and minimum peak crushing force (PCF). Results show that optimization improves the energy absorption characteristics with constrained and unconstrained peak crashing load. Also, it is concluded that the aluminum tube has a better energy absorption capability rather than steel tube at a certain peak crushing force. The results justify that the interaction effects between the honeycomb and column walls greatly improve the energy absorption efficiency. A ranking technique for order preference (TOPSIS) is then used to sort the non-dominated solutions by the preference of decision makers. That is, a multi-criteria decision which consists of MOPSO and TOPSIS is presented to find out a compromise solution for decision makers. Furthermore, local and global sensitivity analyses are performed to assess the effect of design variable values on the SEA and PCF functions in design domain. Based on the sensitivity analysis results, it is concluded that for both models, the helix pitch of the honeycomb core has greater effect on the sensitivity of SEA, while, the core thickness has greater effect on the sensitivity of PCF.

Naringin-loaded Poly(ε-caprolactone)/Gelatin Electrospun Mat as a Potential Wound Dressing: In vitro and In vivo Evaluation

Majid Salehi,Ahmad Vaez,Mahdi Naseri-Nosar,Saeed Farzamfar,Arman Ai,Jafar Ai,Shima Tavakol,Mehrdad Khakbiz,Somayeh Ebrahimi-Barough 한국섬유공학회 2018 Fibers and polymers Vol.19 No.1

In the present study, naringin, a flavonoid isolated from the grape and citrus fruit species, was incorporated with poly(ε-caprolactone)/gelatin composite mats in order to develop a potential wound dressing. The composite mats were prepared by electrospinning of poly(ε-caprolactone)/gelatin (1:1 (w/w)) solution incorporated with 1.50 %, 3 % and 6 % (w/w) of naringin. The electrospun mats were evaluated regarding their morphology, contact angle, water-uptake capacity, water vapor transmission rate, tensile properties, drug release, cellular response and in vivo wound healing activity. The study showed that after 2 weeks, the full-thickness excisional wounds of Wistar rats treated with the naringin-loaded dressings achieved a wound closure of higher than 94 % and the dressing containing 6 % (w/w) naringin had almost 100 %wound closure. The sterile gauze, as the control group, showed nearly 86 % of wound closure after this period of time. Our results provided evidence that supports the possible applicability of naringin-loaded wound dressing for successful wound treatment.

Evaluation of the Frequency of the IL-28 Polymorphism (rs8099917) in Patients with Chronic Hepatitis C Using Zip Nucleic Acid Probes, Kerman, Southeast of Iran

Iranmanesh, Zahra,Mollaie, Hamid Reza,Arabzadeh, Seyed Alimohammad,Zahedi, Mohammad Javad,Fazlalipour, Mehdi,Ebrahimi, Saeede Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.5

Polymorphisms in the region of the interleukin IL-28 gene on chromosome 19 have been related with clearance of hepatitis C virus (HCV), a major human pathogen responsible for chronic hepatitis, cirrhosis and hepatocellular carcinoma. About 3% of the world's population is infected with HCV. The long-term response to therapy is influenced by many host and viral factors, and recent evidence has indicated that some host genetic polymorphisms related to IL-28 are the most powerful predictors of virological response in patients with HCV. This study assessed frequency of the IL-28 polymorphism (rs8099917) in 50 patients (39 men and 11 women) with chronic hepatitis C using ZNA probe real time PCR new method. All patients were tested for genotype of HCV and the HCV viral load. In parallel, the levels of SGOT, SGPT and ALK enzymes were assessed. Treatment using Peg-interferon alpha with ribavirin was conducted for patients and subsequently samples were collected to detect any change in viral load or liver enzyme rates. The overall frequency of the TT allele is 74%, TG allele 20% and GG allele 6% and the percent of patients who had T allele was 84%. Clear reduction in viral load and liver enzymes was reported in patients with the T allele. Especially for genotype 1 which is relatively resistant to treatment, these alleles may have a role in this decline. In conclusion, we showed that IL-28 polymorphism rs8099917 strongly predicts virological response in HCV infection and that real-time PCR with Zip nucleic acid probes is a sensitive, specific and rapid detection method for detection of SNPs which will be essential for monitoring patients undergoing antiviral therapy.