In this paper,drain current transient characteristics ofβ-Ga2O3 high electron mobility transistor(HEMT)are studied to access current collapse and recovery time due to dynamic population and de-population of deep leve...In this paper,drain current transient characteristics ofβ-Ga2O3 high electron mobility transistor(HEMT)are studied to access current collapse and recovery time due to dynamic population and de-population of deep level traps and interface traps.An approximately 10 min,and 1 h of recovery time to steady-state drain current value is measured under 1 ms of stress on the gate and drain electrodes due to iron(Fe)–dopedβ-Ga2O3 substrate and germanium(Ge)–dopedβ-Ga2O3 epitaxial layer respectively.On-state current lag is more severe due to widely reported defect trap EC–0.82 e V over EC–0.78 e V,-0.75 e V present in Iron(Fe)-dopedβ-Ga2O3 bulk crystals.A negligible amount of current degradation is observed in the latter case due to the trap level at EC–0.98 e V.It is found that occupancy of ionized trap density varied mostly under the gate and gate–source area.This investigation of reversible current collapse phenomenon and assessment of recovery time inβ-Ga2O3 HEMT is carried out through 2 D device simulations using appropriate velocity and charge transport models.This work can further help in the proper characterization ofβ-Ga2O3 devices to understand temporary and permanent device degradation.展开更多
Graphene-driving strain-pre-store engineering enables the epitaxy of strain-free AlN film with low dislocation density for DUV-LED and the unique mechanism of strain-relaxation in QvdW epitaxy was demystified.
Purpose:To compare the complications and the recurrence rate between fibrin glue (TISSEEL) and Vicryl 8-0 sutures in amniotic membrane transplant during pterygium surgery.Methods:Patients who underwent pterygium surge...Purpose:To compare the complications and the recurrence rate between fibrin glue (TISSEEL) and Vicryl 8-0 sutures in amniotic membrane transplant during pterygium surgery.Methods:Patients who underwent pterygium surgery with amniotic membrane transplant (AMT) in the Wang Eye Clinic (Doraville,USA).were randomly categorized into two groups:one group received TISSEEL and the other group received Vicryl 8-0 sutures.All procedures for both groups were performed by one ophthalmologist.Twenty-four patients (24 eyes) participated in the TISSEEL group (22 eyes with primary surgery and 2 eyes with surgery for recurrence) and 19 patients (19 eyes) took part in the suture group (18 primary eyes and 1 recurrence).The patients with recurrent pterygium in both groups had not received AMT previously.Post-operatively,patients were followed up for one week and then one year to check for any signs of complications and recurrence.Results:Conjunctival inflammation occurred in 3 eyes (12.5%) in the TISSEEL group,and 6 eyes (31.6%) in the suture group.(P<0.05,Chi-square test).In the TISSEEL group,1 eye (4.2%) showed recurrence,while there were no recurrences in the sutures group.There were 3 dry eyes (15.8%) in the suture group and 2 dry eyes (8.3%) in the TISSEEL group (P>0.05).No dislocated conjunctival grafts,Dellen,inflammation,infection,bleeding,pyogenic granuloma,or scleromalacia was observed in either group.Conclusion:Pterygium surgery with AMT had less conjunctival inflammation and dry eye in patients receiving fibrin glue than those with Vicryl 8-0 sutures.展开更多
Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging,as well as high-pressure gradients in these reservoirs.Polymer may cause pore blo...Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging,as well as high-pressure gradients in these reservoirs.Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine.Low-tension gas(LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity.In LTG flooding,the interfacial tension between oil and water is reduced to ultra-low values(10^-3 dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood.Gas(nitrogen,hydrocarbon gases or C02) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced(oil) and displacing phases,thus improving the displacement efficiency of the oil.In this work,the mechanism governing LTG flooding in low-permeability,high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments.The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality,and how they influence oil mobilization and displacement efficiency.Qualitative assessment of the results was performed by studying oil recovery,oil fractional flow,oil bank breakthrough and effluent salinity and pressure drop characteristics.展开更多
Steam-assisted gravity drainage(SAGD)is a mature technology for bitumen recovery from oil sands.However,it is an energy-intensive process that requires large amounts of steam to heat and mobilize bitumen.The purpose o...Steam-assisted gravity drainage(SAGD)is a mature technology for bitumen recovery from oil sands.However,it is an energy-intensive process that requires large amounts of steam to heat and mobilize bitumen.The purpose of this work is to develop ways to enhance SAGD performance through the use of organic base additives.The research is approached from three focus areas that supplement and guide each other:characterization tests,sand-pack floods,and computational simulation.A number of key mechanisms for enhancing oil recovery were identified,high-temperature additive characterization tests were developed,and promising alkalis were tested in porous media.Simulation was employed to history-match sandpack flood production data,in order to demonstrate the effect of an additive on the oil–water relative permeability.Based on these results,it was concluded that oxygenated organic bases had the most potential for improving bitumen recovery through reducing the oil–water interfacial tension(IFT)by increasing the pH of the system.These organic bases favorably modify the interfacial energies between the immiscible oil–water phases and enable them to flow easily through the porous media during production.Sand-pack flood tests have successfully demonstrated a 10%–15%improvement in bitumen recovery,over baseline,in the presence of IFT-reducing additives.Simulation results further showed that an IFT reduction had a positive impact on SAGD performance.This work demonstrates the potential of organic bases to improve not only SAGD,but other steam injection processes.Furthermore,a number of experimental methods were developed,tried,and tested during the course of this work.展开更多
基金an outcome of the collaborative R&D work undertaken in the project under the Visvesvaraya PhD Scheme of Ministry of Electronics&Information Technology,Govt.of India,being implemented by Digital India Corporation。
文摘In this paper,drain current transient characteristics ofβ-Ga2O3 high electron mobility transistor(HEMT)are studied to access current collapse and recovery time due to dynamic population and de-population of deep level traps and interface traps.An approximately 10 min,and 1 h of recovery time to steady-state drain current value is measured under 1 ms of stress on the gate and drain electrodes due to iron(Fe)–dopedβ-Ga2O3 substrate and germanium(Ge)–dopedβ-Ga2O3 epitaxial layer respectively.On-state current lag is more severe due to widely reported defect trap EC–0.82 e V over EC–0.78 e V,-0.75 e V present in Iron(Fe)-dopedβ-Ga2O3 bulk crystals.A negligible amount of current degradation is observed in the latter case due to the trap level at EC–0.98 e V.It is found that occupancy of ionized trap density varied mostly under the gate and gate–source area.This investigation of reversible current collapse phenomenon and assessment of recovery time inβ-Ga2O3 HEMT is carried out through 2 D device simulations using appropriate velocity and charge transport models.This work can further help in the proper characterization ofβ-Ga2O3 devices to understand temporary and permanent device degradation.
文摘Graphene-driving strain-pre-store engineering enables the epitaxy of strain-free AlN film with low dislocation density for DUV-LED and the unique mechanism of strain-relaxation in QvdW epitaxy was demystified.
文摘Purpose:To compare the complications and the recurrence rate between fibrin glue (TISSEEL) and Vicryl 8-0 sutures in amniotic membrane transplant during pterygium surgery.Methods:Patients who underwent pterygium surgery with amniotic membrane transplant (AMT) in the Wang Eye Clinic (Doraville,USA).were randomly categorized into two groups:one group received TISSEEL and the other group received Vicryl 8-0 sutures.All procedures for both groups were performed by one ophthalmologist.Twenty-four patients (24 eyes) participated in the TISSEEL group (22 eyes with primary surgery and 2 eyes with surgery for recurrence) and 19 patients (19 eyes) took part in the suture group (18 primary eyes and 1 recurrence).The patients with recurrent pterygium in both groups had not received AMT previously.Post-operatively,patients were followed up for one week and then one year to check for any signs of complications and recurrence.Results:Conjunctival inflammation occurred in 3 eyes (12.5%) in the TISSEEL group,and 6 eyes (31.6%) in the suture group.(P<0.05,Chi-square test).In the TISSEEL group,1 eye (4.2%) showed recurrence,while there were no recurrences in the sutures group.There were 3 dry eyes (15.8%) in the suture group and 2 dry eyes (8.3%) in the TISSEEL group (P>0.05).No dislocated conjunctival grafts,Dellen,inflammation,infection,bleeding,pyogenic granuloma,or scleromalacia was observed in either group.Conclusion:Pterygium surgery with AMT had less conjunctival inflammation and dry eye in patients receiving fibrin glue than those with Vicryl 8-0 sutures.
基金supported by Petroleum Development Oman and Shell Global Solutions International。
文摘Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging,as well as high-pressure gradients in these reservoirs.Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine.Low-tension gas(LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity.In LTG flooding,the interfacial tension between oil and water is reduced to ultra-low values(10^-3 dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood.Gas(nitrogen,hydrocarbon gases or C02) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced(oil) and displacing phases,thus improving the displacement efficiency of the oil.In this work,the mechanism governing LTG flooding in low-permeability,high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments.The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality,and how they influence oil mobilization and displacement efficiency.Qualitative assessment of the results was performed by studying oil recovery,oil fractional flow,oil bank breakthrough and effluent salinity and pressure drop characteristics.
基金support of this research from The Dow Chemical Company
文摘Steam-assisted gravity drainage(SAGD)is a mature technology for bitumen recovery from oil sands.However,it is an energy-intensive process that requires large amounts of steam to heat and mobilize bitumen.The purpose of this work is to develop ways to enhance SAGD performance through the use of organic base additives.The research is approached from three focus areas that supplement and guide each other:characterization tests,sand-pack floods,and computational simulation.A number of key mechanisms for enhancing oil recovery were identified,high-temperature additive characterization tests were developed,and promising alkalis were tested in porous media.Simulation was employed to history-match sandpack flood production data,in order to demonstrate the effect of an additive on the oil–water relative permeability.Based on these results,it was concluded that oxygenated organic bases had the most potential for improving bitumen recovery through reducing the oil–water interfacial tension(IFT)by increasing the pH of the system.These organic bases favorably modify the interfacial energies between the immiscible oil–water phases and enable them to flow easily through the porous media during production.Sand-pack flood tests have successfully demonstrated a 10%–15%improvement in bitumen recovery,over baseline,in the presence of IFT-reducing additives.Simulation results further showed that an IFT reduction had a positive impact on SAGD performance.This work demonstrates the potential of organic bases to improve not only SAGD,but other steam injection processes.Furthermore,a number of experimental methods were developed,tried,and tested during the course of this work.
