One of the most severe problems during production from heavy crude oil reservoirs is the formation of asphaltene precipitation and as a result deposition in the tubing,surface facilities and near wellbore region which...One of the most severe problems during production from heavy crude oil reservoirs is the formation of asphaltene precipitation and as a result deposition in the tubing,surface facilities and near wellbore region which causes oil production and permeability reduction in addition to rock wettability alteration in the reservoir.So one of the economical ways to prevent such incidents is using the chemicals which are called asphaltene inhibitor.In this study,the influence of three commercial inhibitors,namely;Cetyl Terimethyl Ammonium Bromide(CTAB),Sodium Dodecyl Sulfate(SDS),Triton X-100 and four non-commercial(Benzene,Benzoic Acid,Salicylic Acid,Naphthalene)inhibitors on two Iranian crude oils were investigated.This study extends previous works and contributes toward the better understanding of interactions between asphaltene and inhibitor.Effect of functional groups and structure of inhibitors on asphaltene precipitation were studied and it seems clear that the nature and polarity of asphaltene(structure and amount of impurities presented)has a significant impact on the selection of inhibitors.asphaltene dispersant tests and Core flood tests were designed for evaluation of inhibitors in static and dynamic conditions.The results revealed distinguished mechanisms for asphaltene solubilization/dispersion(such as hydrogen bonding,pep interaction and acid-base interaction)and influence of additional side group(OH)on inhibition power of inhibitor.During the experiments,it was found that increasing inhibitor concentration may lead to the self-assembly of inhibitor and declining of asphaltene stabilization.So,finding optimum concentration of inhibitor with high efficiency and available at a reasonable price is very important.The results suggest that 600 ppm of CTAB and 300 ppm of SDS were approximately optimum concentrations for the studied crude oils.One of the most important findings that differ from previous studies is the revelation of the mechanism behind the SDS/asphaltene behavior in various concentrations of inhibi展开更多
Adverse effects associated with peginterferon and ribavirin during hepatitis C treatment are well known. Sudden hearing loss has rarely been reported. Possible mechanisms involved include direct ototoxicity of interfe...Adverse effects associated with peginterferon and ribavirin during hepatitis C treatment are well known. Sudden hearing loss has rarely been reported. Possible mechanisms involved include direct ototoxicity of interferon, autoimmunity, and hematological changes. Hearing loss is frequently fully resolved after discontinuation of antiviral therapy. We report a 47-year- old man with chronic hepatitis C, genotype 2 ac who developed sudden hearing loss 22 wk after starting therapy with peginterferon alpha 2a at a dose of 180 ~g per week and ribavirin 800 mg per day. Since symptoms did not worsen, antiviral therapy was continued for 2 wk, according to the patient＇s wish. Hearing loss resolved within 2 wk after the end of treatment. Serum liver alanine aminotransferase remained normal during and after the end of antiviral therapy. HCV RNA was undetectable at the end of therapy and remained negative 24 wk later. Thus, patients should be aware that hearing loss may occur with peginterferon therapy, but the decision whether to continue or to stop the treatment is based on the clinical judgment of the physician and the wishes of the patient.展开更多
In this paper,we study in a constructive way the stabilization problem of fractional bilinear systems with multiple inputs.Using the quadratic Lyapunov functions and some additional hypotheses on the unit sphere,we co...In this paper,we study in a constructive way the stabilization problem of fractional bilinear systems with multiple inputs.Using the quadratic Lyapunov functions and some additional hypotheses on the unit sphere,we construct stabilizing feedback laws for the considered fractional bilinear system.A numerical example is given to illustrate the efficiency of the obtained result.展开更多
In this paper,an analysis for ill conditioning problem in subspace identifcation method is provided.The subspace identifcation technique presents a satisfactory robustness in the parameter estimation of process model ...In this paper,an analysis for ill conditioning problem in subspace identifcation method is provided.The subspace identifcation technique presents a satisfactory robustness in the parameter estimation of process model which performs control.As a frst step,the main geometric and mathematical tools used in subspace identifcation are briefly presented.In the second step,the problem of analyzing ill-conditioning matrices in the subspace identifcation method is considered.To illustrate this situation,a simulation study of an example is introduced to show the ill-conditioning in subspace identifcation.Algorithms numerical subspace state space system identifcation(N4SID)and multivariable output error state space model identifcation(MOESP)are considered to study,the parameters estimation while using the induction motor model,in simulation(Matlab environment).Finally,we show the inadequacy of the oblique projection and validate the efectiveness of the orthogonal projection approach which is needed in ill-conditioning;a real application dealing with induction motor parameters estimation has been experimented.The obtained results proved that the algorithm based on orthogonal projection MOESP,overcomes the situation of ill-conditioning in the Hankel s block,and thereby improving the estimation of parameters.展开更多
Biocomposite films prepared with melt compounding and film blowing have become a new trend in plastic research to deliver more eco-friendly packages.Polylactic acid(PLA)was melt compounded with minimally processed dat...Biocomposite films prepared with melt compounding and film blowing have become a new trend in plastic research to deliver more eco-friendly packages.Polylactic acid(PLA)was melt compounded with minimally processed date palm leaf fiber(DPLF)and converted into films by blown film extrusion.The compounding was done in order to enhance the film mechanical properties in one hand,and to decrease the film production cost in the other hand.In this present study,a reference PLA film and films with 1%,2%,and 5%of DPLF(weight%)were produced with different process parameters.The spatial variations in films thickness and lay flat width indicate that the addition of DPLF up to 2%enhances the bubble stability for the tested process parameters.However,the composite with 5%DPLF shows nearly the same processability window as the neat PLA.The structural and mechanical characterizations of films suggest a reinforcing effect of the PLA matrix up to 2%of fiber(with an optimum at 1%).Larger DPLF loading leads to depressed and more anisotropic mechanical properties,related to an increased density of defects at the fiber-PLA fragile interface and to a DPLF-induced enhanced PLA thermal degradation and amorphous phase orientation.展开更多
The deposition of asphaltenes on the inner wall of oil wells and pipelines causes flow blockage and significant production loss in these conduits.The major underlying mechanism(s)for the deposition of asphaltene parti...The deposition of asphaltenes on the inner wall of oil wells and pipelines causes flow blockage and significant production loss in these conduits.The major underlying mechanism(s)for the deposition of asphaltene particles from the oil stream are still under investigation as an active research topic in the literature.In this work,a new deposition model considering both diffusional and inertial transport of asphaltene toward the tubing surface was developed.Model predictions were compared and verified with two sound experimental data available in the literature to evaluate the model's performance.A parametric study was done using the validated model in order to investigate the effect of the asphaltene particle size,flow velocity and oil viscosity on the magnitude of asphaltene deposition rate.Results of the study revealed that increasing the oil velocity causes more drag force on wall's inner surface;consequently,particles tend to transport away from the surface and the rate of asphaltene deposition is decreased.In addition,the developed model predicts that at low fluid velocity(~0.7 m/s),the less viscous oil is more prone to asphaltene deposition problem.展开更多
Different methods of enhanced oil recovery have been used to produce trapped oil.One of these methods is carbonated water injection in which CO2 contained water is injected in reservoirs in order to decrease free CO2 ...Different methods of enhanced oil recovery have been used to produce trapped oil.One of these methods is carbonated water injection in which CO2 contained water is injected in reservoirs in order to decrease free CO2 injection mobility,increase water viscosity and store/remove produced greenhouse CO2 gas safely.Another enhanced oil recovery method is smart water injection at which the ions in brine are modified in order to make controlled reactions with distributed ions on the surface of rock to cause more hydrocarbon recovery.Therefore,combination of these two methods may also have a great effect on enhancing oil recovery or may result in recovery factor less than each method used alone.In this paper hybrid smart carbonated water injection method is investigated to study its applicability in oil recovery using core flooding setup.The experimental core flooding setup was designed to perform different types of EOR methods for the sake of recovery comparison with the new hybrid method.The effect of both brine content and volume of CO2 is determining in hybrid EOR assessment.The main findings of this work show that the hybrid smart carbonated water results in the highest recovery factor in comparison to the most well-known EOR methods for carbonate cores.展开更多
Fibre-matrix interface is known to have contribution to the mechanical performance of fibre-reinforced composite by its potential for load transfer between the fibre and the matrix. Such load transfer is of great impo...Fibre-matrix interface is known to have contribution to the mechanical performance of fibre-reinforced composite by its potential for load transfer between the fibre and the matrix. Such load transfer is of great importance in dentistry when a post is used for fixing a ceramic crown on the tooth. In this study, a pull-out test was carried out to analyse the interfacial properties of a steel fibre embedded in a polyester and epoxy matrices. It was found that the fibre-matrix interface is debonded on the whole embedded length when the fibre stress reached the debonding stress. Then, the fibre stress fell down to the initial extraction stress required to pulling out the debonded fibre from the matrix. Both debonding stress and initial extraction stress initiated a linear increase with the implantation length after the debonding stress reached horizontal asymptotes. To analyse the fibre-matrix load transfer before debonding, an analytical shear-lag model was adopted to in this test conditions. Fitting the experimental results with the analytical model provided the interfacial shear strength. By considering the Coulomb friction at the fibre-matrix interface during the fibre extraction process, an analytical model which considers Poisson＇s effects on both fibre and matrix, was developed. In this model, knowledge of the initial extraction stress of the fibre provides the residual normal stress at the fibre-matrix interface.展开更多
In this paper we elaborate a general expression of the conditional expectation related to pricing problem of the American options using the Malliavin derivative （without localization）. This work is a generalization ...In this paper we elaborate a general expression of the conditional expectation related to pricing problem of the American options using the Malliavin derivative （without localization）. This work is a generalization of paper of Bally et al. （2005） [ 1 ] for the one dimensional case. Basing on the density function of the asset price, Bally and al. used the Malliavin calculus to evaluate the conditional expectation related to pricing American option problem, but in our work we use the Malliavin derivative to resolve the previous problem.展开更多
Transient rate decline curve analysis for constant pressure production is presented in this pa- per for a naturally fractured reservoir. This approach is based on exponential and constant bottom-hole pressure solution...Transient rate decline curve analysis for constant pressure production is presented in this pa- per for a naturally fractured reservoir. This approach is based on exponential and constant bottom-hole pressure solution. Based on this method, when In （flow rate） is plotted versus time, two straight lines are ob- tained which can be used for estimating different parameters of a naturally fractured reservoir. Parameters such as storage capacity ratio （co）, reservoir drainage area （A）, reservoir shape factor （CA）, fracture per- meability （ky）, interporosity flow parameter （,~） and the other parameters can be determined by this ap- proach. The equations are based on a model originally presented by Warren and Root and extended by Da Prat et al. and Mavor and Cinco-Ley. The proposed method has been developed to be used for naturally fractured reservoirs with different geometries. This method does not involve the use of any chart and by us- ing the pseudo steady state flow regime, the influence of wellbore storage on the value of the parameters ob- tained from this technique is negligible. In this technique, all the parameters can be obtained directly while in conventional approaches like type curve matching method, parameters such as co and g should be ob- tained by other methods like build-up test analysis and this is one of the most important advantages of this method that could save time during reservoir analyses. Different simulated and field examples were used for testing the proposed technique. Comparison between the obtained results by this approach and the results of type curve matching method shows a high performance of decline curves in well testing.展开更多
Asphaltenes are complex molecular entities, which together with resins, aromatic hydrocarbons and saturates forms the crude oil. Asphaltenes and resins are in the thermodynamic equilibrium at static reservoir conditio...Asphaltenes are complex molecular entities, which together with resins, aromatic hydrocarbons and saturates forms the crude oil. Asphaltenes and resins are in the thermodynamic equilibrium at static reservoir condition. However, asphaltene can precipitate due to changes in thermodynamic condition. Asphaltene deposition in production tubings has been an outstanding problem with wide economic impact on the oil industry. Meanwhile, the use of real-time tools to monitor depositions along the well is of great difficulty. In this work, the asphaltene precipitation region in a single phase flow wellbore is predicted for an oil well of the Iranian oil field. Then, asphaltene deposition thickness along the well is predicted for three time intervals. The simulation results indicated that asphaltene thickness exceeded more than 50% of tubing radius;therefore, a reduction in flow rate, an increase in pressure drop and tubing blockage are expected. Moreover, it is shown the deposits thickness along the wellbore has approximately a skew normal distribution shape, which could be the result of increases in velocity and excess pressure drop.展开更多
Effect of initial interference fit on pull-out strength in cementless fixation between bovine tibia and smooth stainless steel post was investigated in this study. Compressive behavior of bovine spongious bone was stu...Effect of initial interference fit on pull-out strength in cementless fixation between bovine tibia and smooth stainless steel post was investigated in this study. Compressive behavior of bovine spongious bone was studied using mechanical testing in order to evaluate the elastic-plastic properties in different regions of the proximal tibia. Friction tests were carried out in the aim to evaluate the friction behavior of the contact between bovine spongious bone and stainless steel. A cylindrical stainless steel post inserted in a pre-drilled bovine tibia with an initial interference fit was taken as an in vitro model to assess the contribution of post fixation to the initial stability of the Total Knee Arthroplasty （TKA） tibial component. Pull-out experiments were carried out for different initial interference fits. Finite Element Models （FEM） using local elastic-plastic properties of the bovine bone were developed for the analysis of the experimental ultimate pull-out force results. At the post/bone interface, Coulomb friction was considered in the FEM calculations with pressure-dependent friction coefficient. It was found that the FEM results of the ultimate force are in good agreement with the experimental results. The analysis of the FEM interfacial stresses indicates that the micro-slip initiation depends on the local bone properties.展开更多
In this work, a friction and wear simulator was used to reproduce the Anterior-Posterior （AP） sliding and the Flex- ion-Extension （FE） rotation generated in the knee joint during human gait cycle. We chose to simp...In this work, a friction and wear simulator was used to reproduce the Anterior-Posterior （AP） sliding and the Flex- ion-Extension （FE） rotation generated in the knee joint during human gait cycle. We chose to simplify the contact geometry between the Total Knee Arthroplasty （TKA） femoral component and tibial insert. A 304L stainless steel cylinder which replaces the femoral component was loaded onto a flat High Density Polyethylene （HDPE） block which replaces the tibial insert. The tribological behavior of the considered contact was analyzed by tracking the number of cycles, the friction coefficient, the roughness of the wear track on HDPE, the HDPE weight loss and the damage mechanisms. The friction coefficient shows a gradual increase with the number of cycles for both AP and FE kinematics. The evolution of friction coefficient with the number of cycles is not affected by the value of the imposed normal load in the case of AP sliding. For the FE rotation, decreased friction coefficient is obtained when the imposed normal load increases. For both considered AP and FE kinematics, the roughness of the wear track on the HDPE is not affected by the imposed normal load. It shows a progressive decrease when the number of cycles increases. The wear of HDPE obeys the Archard law and the wear coefficient increases with the normal force. For a given value of normal load, the obtained wear coefficient for the AP sliding is larger than that obtained for FE rotation. A predominant adhesive wear mechanism was identified for both AP and FE kinematics. Under the same normal load, damage development in terms of plastic deformation, micro-cracking and debonding is more pronounced for the AP sliding if compared with the FE rotation. For a given kinematics, the damage severity increases with the normal load. This finding is in good agreement with the predicted values of the wear coefficient according to the Archard law.展开更多
Introduction: The concept of clopidogrel resistance, first described in biology is being strengthened by recent data from clinical epidemiology. The cardiologists have been sensitized to this concept because of its po...Introduction: The concept of clopidogrel resistance, first described in biology is being strengthened by recent data from clinical epidemiology. The cardiologists have been sensitized to this concept because of its possible involvement in the occurrence of coronary stent thrombosis. Purpose of the study: The purpose of this study was to investigate the genetic variant of the gene CYP 2C19 inour population and to assess the involvement of this genetic profile in the occurrence of major cardiovascular events (MACE) during the follow-up period. Methods: Our prospective study was conducted between May 2009 and September 2010 including 100 patients admitted to the cardiology department for percutaneous coronary stenting. The patients were divided into 2 groups: those with at least one CYP2C19*2 allele (*2 carriers) and non-carriers. Results: The mean age of our patients was 56.7 years ± 10, 5. No remarkable differences in the baseline characteristics were noted between the two groups. The prevalence of CYP2C19*2 allele in our population was 11.5%. Hospital mortality was estimated at 3%. No statistically significant differences were noted between the two groups regarding the occurrence of intra hospital MACE. The mean follow up was 7.5 ± 4.87 months for the entire study population. The rate of MACE during the follow-up of patients receiving clopidogrel was 8.2% throughout the study population: 5.3% in the *2 non-carriers versus 18.2% in the *2 carriers with a statistically significant difference (p = 0.075) at the risk of error of 10%. Concerning the occurrence of stent thrombosis, there was no significant statistical difference between the two study groups. Conclusion: From these results it is suggested that CYP2C19*2 polymorphism is associated with increase in the occurrence of MACE among Tunisian patients receiving clopidogrel. A larger study is needed to assess the role of genotyping in the evaluation of the phenomenon of clopidogrel resistance.展开更多
We report for the first time the occurrence of Trisetacus acari Eriophyoid parasite infesting Juniperus excelsa seeds in Lebanon. The specimen studied belong most probably to the species T. kirghizorum (Shevchenko 196...We report for the first time the occurrence of Trisetacus acari Eriophyoid parasite infesting Juniperus excelsa seeds in Lebanon. The specimen studied belong most probably to the species T. kirghizorum (Shevchenko 1962) living on J. semiglobosa in the Kirghiz mountains. We suggest that Trisetacus spp. found in the seed cones of Kirghiz junipers as well as J. excelsa comprise a complex of cryptic species that might be distinguished using molecular markers. It is necessary to revise the group cupressi in the genus Trisetacus and an integrated phylogenetic study of the mites belonging to this genus could elucidate the patterns of eriophyoid mites evolution on conifers and could help in a better resolution of the Juniper phylogeny.展开更多
基金The authors would like to thank the Research Department of Ahwaz Petroleum University and National Iranian South Oil Company(NISOC)for supporting this study。
文摘One of the most severe problems during production from heavy crude oil reservoirs is the formation of asphaltene precipitation and as a result deposition in the tubing,surface facilities and near wellbore region which causes oil production and permeability reduction in addition to rock wettability alteration in the reservoir.So one of the economical ways to prevent such incidents is using the chemicals which are called asphaltene inhibitor.In this study,the influence of three commercial inhibitors,namely;Cetyl Terimethyl Ammonium Bromide(CTAB),Sodium Dodecyl Sulfate(SDS),Triton X-100 and four non-commercial(Benzene,Benzoic Acid,Salicylic Acid,Naphthalene)inhibitors on two Iranian crude oils were investigated.This study extends previous works and contributes toward the better understanding of interactions between asphaltene and inhibitor.Effect of functional groups and structure of inhibitors on asphaltene precipitation were studied and it seems clear that the nature and polarity of asphaltene(structure and amount of impurities presented)has a significant impact on the selection of inhibitors.asphaltene dispersant tests and Core flood tests were designed for evaluation of inhibitors in static and dynamic conditions.The results revealed distinguished mechanisms for asphaltene solubilization/dispersion(such as hydrogen bonding,pep interaction and acid-base interaction)and influence of additional side group(OH)on inhibition power of inhibitor.During the experiments,it was found that increasing inhibitor concentration may lead to the self-assembly of inhibitor and declining of asphaltene stabilization.So,finding optimum concentration of inhibitor with high efficiency and available at a reasonable price is very important.The results suggest that 600 ppm of CTAB and 300 ppm of SDS were approximately optimum concentrations for the studied crude oils.One of the most important findings that differ from previous studies is the revelation of the mechanism behind the SDS/asphaltene behavior in various concentrations of inhibi
文摘Adverse effects associated with peginterferon and ribavirin during hepatitis C treatment are well known. Sudden hearing loss has rarely been reported. Possible mechanisms involved include direct ototoxicity of interferon, autoimmunity, and hematological changes. Hearing loss is frequently fully resolved after discontinuation of antiviral therapy. We report a 47-year- old man with chronic hepatitis C, genotype 2 ac who developed sudden hearing loss 22 wk after starting therapy with peginterferon alpha 2a at a dose of 180 ~g per week and ribavirin 800 mg per day. Since symptoms did not worsen, antiviral therapy was continued for 2 wk, according to the patient＇s wish. Hearing loss resolved within 2 wk after the end of treatment. Serum liver alanine aminotransferase remained normal during and after the end of antiviral therapy. HCV RNA was undetectable at the end of therapy and remained negative 24 wk later. Thus, patients should be aware that hearing loss may occur with peginterferon therapy, but the decision whether to continue or to stop the treatment is based on the clinical judgment of the physician and the wishes of the patient.
文摘In this paper,we study in a constructive way the stabilization problem of fractional bilinear systems with multiple inputs.Using the quadratic Lyapunov functions and some additional hypotheses on the unit sphere,we construct stabilizing feedback laws for the considered fractional bilinear system.A numerical example is given to illustrate the efficiency of the obtained result.
基金supported by the Ministry of Higher Education and Scientific Research of Tunisia
文摘In this paper,an analysis for ill conditioning problem in subspace identifcation method is provided.The subspace identifcation technique presents a satisfactory robustness in the parameter estimation of process model which performs control.As a frst step,the main geometric and mathematical tools used in subspace identifcation are briefly presented.In the second step,the problem of analyzing ill-conditioning matrices in the subspace identifcation method is considered.To illustrate this situation,a simulation study of an example is introduced to show the ill-conditioning in subspace identifcation.Algorithms numerical subspace state space system identifcation(N4SID)and multivariable output error state space model identifcation(MOESP)are considered to study,the parameters estimation while using the induction motor model,in simulation(Matlab environment).Finally,we show the inadequacy of the oblique projection and validate the efectiveness of the orthogonal projection approach which is needed in ill-conditioning;a real application dealing with induction motor parameters estimation has been experimented.The obtained results proved that the algorithm based on orthogonal projection MOESP,overcomes the situation of ill-conditioning in the Hankel s block,and thereby improving the estimation of parameters.
文摘Biocomposite films prepared with melt compounding and film blowing have become a new trend in plastic research to deliver more eco-friendly packages.Polylactic acid(PLA)was melt compounded with minimally processed date palm leaf fiber(DPLF)and converted into films by blown film extrusion.The compounding was done in order to enhance the film mechanical properties in one hand,and to decrease the film production cost in the other hand.In this present study,a reference PLA film and films with 1%,2%,and 5%of DPLF(weight%)were produced with different process parameters.The spatial variations in films thickness and lay flat width indicate that the addition of DPLF up to 2%enhances the bubble stability for the tested process parameters.However,the composite with 5%DPLF shows nearly the same processability window as the neat PLA.The structural and mechanical characterizations of films suggest a reinforcing effect of the PLA matrix up to 2%of fiber(with an optimum at 1%).Larger DPLF loading leads to depressed and more anisotropic mechanical properties,related to an increased density of defects at the fiber-PLA fragile interface and to a DPLF-induced enhanced PLA thermal degradation and amorphous phase orientation.
文摘The deposition of asphaltenes on the inner wall of oil wells and pipelines causes flow blockage and significant production loss in these conduits.The major underlying mechanism(s)for the deposition of asphaltene particles from the oil stream are still under investigation as an active research topic in the literature.In this work,a new deposition model considering both diffusional and inertial transport of asphaltene toward the tubing surface was developed.Model predictions were compared and verified with two sound experimental data available in the literature to evaluate the model's performance.A parametric study was done using the validated model in order to investigate the effect of the asphaltene particle size,flow velocity and oil viscosity on the magnitude of asphaltene deposition rate.Results of the study revealed that increasing the oil velocity causes more drag force on wall's inner surface;consequently,particles tend to transport away from the surface and the rate of asphaltene deposition is decreased.In addition,the developed model predicts that at low fluid velocity(~0.7 m/s),the less viscous oil is more prone to asphaltene deposition problem.
文摘Different methods of enhanced oil recovery have been used to produce trapped oil.One of these methods is carbonated water injection in which CO2 contained water is injected in reservoirs in order to decrease free CO2 injection mobility,increase water viscosity and store/remove produced greenhouse CO2 gas safely.Another enhanced oil recovery method is smart water injection at which the ions in brine are modified in order to make controlled reactions with distributed ions on the surface of rock to cause more hydrocarbon recovery.Therefore,combination of these two methods may also have a great effect on enhancing oil recovery or may result in recovery factor less than each method used alone.In this paper hybrid smart carbonated water injection method is investigated to study its applicability in oil recovery using core flooding setup.The experimental core flooding setup was designed to perform different types of EOR methods for the sake of recovery comparison with the new hybrid method.The effect of both brine content and volume of CO2 is determining in hybrid EOR assessment.The main findings of this work show that the hybrid smart carbonated water results in the highest recovery factor in comparison to the most well-known EOR methods for carbonate cores.
文摘Fibre-matrix interface is known to have contribution to the mechanical performance of fibre-reinforced composite by its potential for load transfer between the fibre and the matrix. Such load transfer is of great importance in dentistry when a post is used for fixing a ceramic crown on the tooth. In this study, a pull-out test was carried out to analyse the interfacial properties of a steel fibre embedded in a polyester and epoxy matrices. It was found that the fibre-matrix interface is debonded on the whole embedded length when the fibre stress reached the debonding stress. Then, the fibre stress fell down to the initial extraction stress required to pulling out the debonded fibre from the matrix. Both debonding stress and initial extraction stress initiated a linear increase with the implantation length after the debonding stress reached horizontal asymptotes. To analyse the fibre-matrix load transfer before debonding, an analytical shear-lag model was adopted to in this test conditions. Fitting the experimental results with the analytical model provided the interfacial shear strength. By considering the Coulomb friction at the fibre-matrix interface during the fibre extraction process, an analytical model which considers Poisson＇s effects on both fibre and matrix, was developed. In this model, knowledge of the initial extraction stress of the fibre provides the residual normal stress at the fibre-matrix interface.
文摘In this paper we elaborate a general expression of the conditional expectation related to pricing problem of the American options using the Malliavin derivative （without localization）. This work is a generalization of paper of Bally et al. （2005） [ 1 ] for the one dimensional case. Basing on the density function of the asset price, Bally and al. used the Malliavin calculus to evaluate the conditional expectation related to pricing American option problem, but in our work we use the Malliavin derivative to resolve the previous problem.
文摘Transient rate decline curve analysis for constant pressure production is presented in this pa- per for a naturally fractured reservoir. This approach is based on exponential and constant bottom-hole pressure solution. Based on this method, when In （flow rate） is plotted versus time, two straight lines are ob- tained which can be used for estimating different parameters of a naturally fractured reservoir. Parameters such as storage capacity ratio （co）, reservoir drainage area （A）, reservoir shape factor （CA）, fracture per- meability （ky）, interporosity flow parameter （,~） and the other parameters can be determined by this ap- proach. The equations are based on a model originally presented by Warren and Root and extended by Da Prat et al. and Mavor and Cinco-Ley. The proposed method has been developed to be used for naturally fractured reservoirs with different geometries. This method does not involve the use of any chart and by us- ing the pseudo steady state flow regime, the influence of wellbore storage on the value of the parameters ob- tained from this technique is negligible. In this technique, all the parameters can be obtained directly while in conventional approaches like type curve matching method, parameters such as co and g should be ob- tained by other methods like build-up test analysis and this is one of the most important advantages of this method that could save time during reservoir analyses. Different simulated and field examples were used for testing the proposed technique. Comparison between the obtained results by this approach and the results of type curve matching method shows a high performance of decline curves in well testing.
文摘Asphaltenes are complex molecular entities, which together with resins, aromatic hydrocarbons and saturates forms the crude oil. Asphaltenes and resins are in the thermodynamic equilibrium at static reservoir condition. However, asphaltene can precipitate due to changes in thermodynamic condition. Asphaltene deposition in production tubings has been an outstanding problem with wide economic impact on the oil industry. Meanwhile, the use of real-time tools to monitor depositions along the well is of great difficulty. In this work, the asphaltene precipitation region in a single phase flow wellbore is predicted for an oil well of the Iranian oil field. Then, asphaltene deposition thickness along the well is predicted for three time intervals. The simulation results indicated that asphaltene thickness exceeded more than 50% of tubing radius;therefore, a reduction in flow rate, an increase in pressure drop and tubing blockage are expected. Moreover, it is shown the deposits thickness along the wellbore has approximately a skew normal distribution shape, which could be the result of increases in velocity and excess pressure drop.
文摘Effect of initial interference fit on pull-out strength in cementless fixation between bovine tibia and smooth stainless steel post was investigated in this study. Compressive behavior of bovine spongious bone was studied using mechanical testing in order to evaluate the elastic-plastic properties in different regions of the proximal tibia. Friction tests were carried out in the aim to evaluate the friction behavior of the contact between bovine spongious bone and stainless steel. A cylindrical stainless steel post inserted in a pre-drilled bovine tibia with an initial interference fit was taken as an in vitro model to assess the contribution of post fixation to the initial stability of the Total Knee Arthroplasty （TKA） tibial component. Pull-out experiments were carried out for different initial interference fits. Finite Element Models （FEM） using local elastic-plastic properties of the bovine bone were developed for the analysis of the experimental ultimate pull-out force results. At the post/bone interface, Coulomb friction was considered in the FEM calculations with pressure-dependent friction coefficient. It was found that the FEM results of the ultimate force are in good agreement with the experimental results. The analysis of the FEM interfacial stresses indicates that the micro-slip initiation depends on the local bone properties.
文摘In this work, a friction and wear simulator was used to reproduce the Anterior-Posterior （AP） sliding and the Flex- ion-Extension （FE） rotation generated in the knee joint during human gait cycle. We chose to simplify the contact geometry between the Total Knee Arthroplasty （TKA） femoral component and tibial insert. A 304L stainless steel cylinder which replaces the femoral component was loaded onto a flat High Density Polyethylene （HDPE） block which replaces the tibial insert. The tribological behavior of the considered contact was analyzed by tracking the number of cycles, the friction coefficient, the roughness of the wear track on HDPE, the HDPE weight loss and the damage mechanisms. The friction coefficient shows a gradual increase with the number of cycles for both AP and FE kinematics. The evolution of friction coefficient with the number of cycles is not affected by the value of the imposed normal load in the case of AP sliding. For the FE rotation, decreased friction coefficient is obtained when the imposed normal load increases. For both considered AP and FE kinematics, the roughness of the wear track on the HDPE is not affected by the imposed normal load. It shows a progressive decrease when the number of cycles increases. The wear of HDPE obeys the Archard law and the wear coefficient increases with the normal force. For a given value of normal load, the obtained wear coefficient for the AP sliding is larger than that obtained for FE rotation. A predominant adhesive wear mechanism was identified for both AP and FE kinematics. Under the same normal load, damage development in terms of plastic deformation, micro-cracking and debonding is more pronounced for the AP sliding if compared with the FE rotation. For a given kinematics, the damage severity increases with the normal load. This finding is in good agreement with the predicted values of the wear coefficient according to the Archard law.
文摘Introduction: The concept of clopidogrel resistance, first described in biology is being strengthened by recent data from clinical epidemiology. The cardiologists have been sensitized to this concept because of its possible involvement in the occurrence of coronary stent thrombosis. Purpose of the study: The purpose of this study was to investigate the genetic variant of the gene CYP 2C19 inour population and to assess the involvement of this genetic profile in the occurrence of major cardiovascular events (MACE) during the follow-up period. Methods: Our prospective study was conducted between May 2009 and September 2010 including 100 patients admitted to the cardiology department for percutaneous coronary stenting. The patients were divided into 2 groups: those with at least one CYP2C19*2 allele (*2 carriers) and non-carriers. Results: The mean age of our patients was 56.7 years ± 10, 5. No remarkable differences in the baseline characteristics were noted between the two groups. The prevalence of CYP2C19*2 allele in our population was 11.5%. Hospital mortality was estimated at 3%. No statistically significant differences were noted between the two groups regarding the occurrence of intra hospital MACE. The mean follow up was 7.5 ± 4.87 months for the entire study population. The rate of MACE during the follow-up of patients receiving clopidogrel was 8.2% throughout the study population: 5.3% in the *2 non-carriers versus 18.2% in the *2 carriers with a statistically significant difference (p = 0.075) at the risk of error of 10%. Concerning the occurrence of stent thrombosis, there was no significant statistical difference between the two study groups. Conclusion: From these results it is suggested that CYP2C19*2 polymorphism is associated with increase in the occurrence of MACE among Tunisian patients receiving clopidogrel. A larger study is needed to assess the role of genotyping in the evaluation of the phenomenon of clopidogrel resistance.
文摘We report for the first time the occurrence of Trisetacus acari Eriophyoid parasite infesting Juniperus excelsa seeds in Lebanon. The specimen studied belong most probably to the species T. kirghizorum (Shevchenko 1962) living on J. semiglobosa in the Kirghiz mountains. We suggest that Trisetacus spp. found in the seed cones of Kirghiz junipers as well as J. excelsa comprise a complex of cryptic species that might be distinguished using molecular markers. It is necessary to revise the group cupressi in the genus Trisetacus and an integrated phylogenetic study of the mites belonging to this genus could elucidate the patterns of eriophyoid mites evolution on conifers and could help in a better resolution of the Juniper phylogeny.
