Copper-manganese-aluminum （CMA） alloys, containing small additions of Fe, Ni, and Si, exhibit good strength and remarkable corrosion resistance against sea water. The alloys are used in as-cast condition, and their ...Copper-manganese-aluminum （CMA） alloys, containing small additions of Fe, Ni, and Si, exhibit good strength and remarkable corrosion resistance against sea water. The alloys are used in as-cast condition, and their microstructure can show wide variations. The morphology, crystallography and composition of the phases presented in an as-cast （CMA） alloy of nominal composition Cu-14%Mn-8%Al-3%Fe-2%Ni were investigated using optical, electron optical, and microprobe analytical techniques. The as-cast microstructure consisted of the grains of fcc α and bcc β-phases alongwith intermetallic precipitates of various morphologies. The room temperature microstructure exhibited four different types of precipitates inside the α-grains： the ＇large＇ dendritic-shaped particles and the cuboid-shaped precipitates, which were rich in Fe and Mn and had an fcc structure, while the ＇small＇ dendritic-shaped particles and the globular precipitates were based on FeaAI and had DO3 structure. These four different morphologies of intermetallic precipitates exhibited discrete orientation-relationships with the α-matrix. The β-grains only contained very small cuboid shaped precipitates, which could only be resolved through transmission electron microscopy. These precipitates were found to be based on Fe3Al and had the DO3 structure.展开更多
The unavailability of wasted energy due to the irreversibility in the process is called the entropy generation.An irreversible process is a process in which the entropy of the system is increased.The second law of the...The unavailability of wasted energy due to the irreversibility in the process is called the entropy generation.An irreversible process is a process in which the entropy of the system is increased.The second law of thermodynamics is used to define whether the given system is reversible or irreversible.Here,our focus is how to reduce the entropy of the system and maximize the capability of the system.There are many methods for maximizing the capacity of heat transport.The constant pressure gradient or motion of the wall can be used to increase the heat transfer rate and minimize the entropy.The objective of this study is to analyze the heat and mass transfer of an Eyring-Powell fluid in a porous channel.For this,we choose two different fluid models,namely,the plane and generalized Couette flows.The flow is generated in the channel due to a pressure gradient or with the moving of the upper lid.The present analysis shows the effects of the fluid parameters on the velocity,the temperature,the entropy generation,and the Bejan number.The nonlinear boundary value problem of the flow problem is solved with the help of the regular perturbation method.To validate the perturbation solution,a numerical solution is also obtained with the help of the built-in command NDSolve of MATHEMATICA 11.0.The velocity profile shows the shear thickening behavior via first-order Eyring-Powell parameters.It is also observed that the profile of the Bejan number has a decreasing trend against the Brinkman number.Whenηi→0(i=1,2,3),the Eyring-Powell fluid is transformed into a Newtonian fluid.展开更多
We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser(TDFL)using a newly devel-oped single-wall carbon nanotube-based saturable absorber.The TDFL generates the 25 th harmonic mode-locked str...We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser(TDFL)using a newly devel-oped single-wall carbon nanotube-based saturable absorber.The TDFL generates the 25 th harmonic mode-locked stretched pulse train with a high repetition rate of 213MHz and a pulse duration of 710fs.The laser operates at 1901.6nm with an average power of 1.89mW,which corresponds to the pulse energy of 0.008nJ,at 1552nm pump power of 719mW.The peak-to-background ratio is measured to be 60dB,which indicates the stability of the laser.展开更多
We demonstrate a simple,compact and low-cost mode-locked erbium-doped fiber laser(EDFL)using a single-wall carbon nanotube(SWCNT)poly-ethylene oxide(PEO)composite as a passive saturable absorber(SA).The composite with...We demonstrate a simple,compact and low-cost mode-locked erbium-doped fiber laser(EDFL)using a single-wall carbon nanotube(SWCNT)poly-ethylene oxide(PEO)composite as a passive saturable absorber(SA).The composite with an SWCNT concentration of 18wt%is prepared by mixing the SWCNT homogeneous solution with a diluted PEO polymer solution.A droplet of the polymer composite is applied on the fiber ferrule end,which is then mated to another clean ferrule connector to construct an SA.The SA is then integrated into the laser system to self-start stable mode locking at 1557 nm without employing a polarization controller.The EDFL generates a stable soliton pulse train with a duration of 0.81 ps,repetition rate of 44 MHz and average output power of 92.4μW at a 980 nm pump power of 26.8 mW.The soliton laser starts to lase at a pump power threshold of 14.6 mW.展开更多
We demonstrate a simple,compact and low cost Q-switched erbium-doped fiber laser(EDFL)using single-wall carbon nanotubes(CNTs)as a saturable absorber for possible applications in metrology,sensing,and medical diagnost...We demonstrate a simple,compact and low cost Q-switched erbium-doped fiber laser(EDFL)using single-wall carbon nanotubes(CNTs)as a saturable absorber for possible applications in metrology,sensing,and medical diagnostics.The EDFL operates at around 1560 nm with repetition rates of 16.1 kHz and 6.4 kHz with saturable absorbers SA1 and SA2 at a pump power of 120 mW.The absorbers are constructed by optically driven deposition and normal deposition techniques.It is observed that the optical deposition method produces a Q-switched EDFL with a lower threshold of 70 mW and better Q-switching performance compared to that of the normal deposition method.The EDFL also has pulse energy of 90.3 nJ and pulse width of 11.6μs at 120 mW pump power.展开更多
The thermal shock and fatigue behavior of pressureless sintered Al_(2)O_(3)-SiO_(2)-ZrO_(2)(ASZ)composites was studied.The influence of the thermal shock and fatigue on the strengthening response of ASZ has been inves...The thermal shock and fatigue behavior of pressureless sintered Al_(2)O_(3)-SiO_(2)-ZrO_(2)(ASZ)composites was studied.The influence of the thermal shock and fatigue on the strengthening response of ASZ has been investigated by measuring the strength retention and microstructural changes.The magnitude of the flexural strength and fracture of the ASZ has been compared with that of the monolithic Al_(2)O_(3)(A)and Al_(2)O_(3)-SiO_(2)-ZrO_(2)(AZ)composites under the same experimental conditions.Results indicated that the ASZ composites possess the highest resistance against thermal shock and fatigue,in comparison with A and AZ.The improvements were attributed to the enhancement in the fracture toughness of ASZ and the presence of multi-phase reinforcement.展开更多
We propose a Q-switched Er-doped fiber laser （EDFL） with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol （PVA） thin film as a passive saturable absorber （SA）. The SA ...We propose a Q-switched Er-doped fiber laser （EDFL） with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol （PVA） thin film as a passive saturable absorber （SA）. The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 roW. At maximum 1480 nm pump power of 33.0 roW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56/as. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 roW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.展开更多
A Q-switched ytterbium-doped fiber laser （YDFL） is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide （MWCNTs-PEO） film as a passive saturable absorber （SA）. The s...A Q-switched ytterbium-doped fiber laser （YDFL） is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide （MWCNTs-PEO） film as a passive saturable absorber （SA）. The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation. The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW. The YDFL generates a stable pulse train with repetition rates ranging from 7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW. At 59.55-mW pump power, the lowest pulse width and the highest pulse energy are obtained at 12.18 μs and 143.5 n J, respectively.展开更多
We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber （TDF） laser, a homemade double-clad thulium-ytterbium co-doped fiber （TYDF） as the gain ...We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber （TDF） laser, a homemade double-clad thulium-ytterbium co-doped fiber （TYDF） as the gain media, and a multi-walled carbon nanotube （MWCNT） based saturable absorber （SA）. We prepare the MWCNT composite by mixing a homogeneous solution of MWCNTs with a diluted polyvinyl alcohol （PVA） polymer solution and then drying it at room temperature to form a film. The film is placed between two fiber connectors as a SA before it is integrated into a laser ring cavity. The cavity consists of a 2 m long TDF pumped by a 800 nm laser diode and a 15 m long homemade TYDF pumped by a 905 nm multimode laser diode. A stable mode-locking pulse with a repetition rate of 34.6 MHz and a pulse width of 10.79 ps is obtained when the 905 nm multimode pump power reaches 1.8-2.2 W, while the single-mode 800 nm pump power is fixed at 141.5 mW at all times. To the best of our knowledge, this is the first reported mode-locked fiber laser using a MWCNT-based SA.展开更多
We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thulium- bismuth co-doped fiber （TBF） as a gain medium in conjunction with a carbon nanotube （CNT）-based saturable absorbe...We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thulium- bismuth co-doped fiber （TBF） as a gain medium in conjunction with a carbon nanotube （CNT）-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 roW.展开更多
文摘Copper-manganese-aluminum （CMA） alloys, containing small additions of Fe, Ni, and Si, exhibit good strength and remarkable corrosion resistance against sea water. The alloys are used in as-cast condition, and their microstructure can show wide variations. The morphology, crystallography and composition of the phases presented in an as-cast （CMA） alloy of nominal composition Cu-14%Mn-8%Al-3%Fe-2%Ni were investigated using optical, electron optical, and microprobe analytical techniques. The as-cast microstructure consisted of the grains of fcc α and bcc β-phases alongwith intermetallic precipitates of various morphologies. The room temperature microstructure exhibited four different types of precipitates inside the α-grains： the ＇large＇ dendritic-shaped particles and the cuboid-shaped precipitates, which were rich in Fe and Mn and had an fcc structure, while the ＇small＇ dendritic-shaped particles and the globular precipitates were based on FeaAI and had DO3 structure. These four different morphologies of intermetallic precipitates exhibited discrete orientation-relationships with the α-matrix. The β-grains only contained very small cuboid shaped precipitates, which could only be resolved through transmission electron microscopy. These precipitates were found to be based on Fe3Al and had the DO3 structure.
基金Project supported by the National Natural Science Foundation of China(Nos.11971142,11871202,61673169,11701176,11626101,and 11601485)。
文摘The unavailability of wasted energy due to the irreversibility in the process is called the entropy generation.An irreversible process is a process in which the entropy of the system is increased.The second law of thermodynamics is used to define whether the given system is reversible or irreversible.Here,our focus is how to reduce the entropy of the system and maximize the capability of the system.There are many methods for maximizing the capacity of heat transport.The constant pressure gradient or motion of the wall can be used to increase the heat transfer rate and minimize the entropy.The objective of this study is to analyze the heat and mass transfer of an Eyring-Powell fluid in a porous channel.For this,we choose two different fluid models,namely,the plane and generalized Couette flows.The flow is generated in the channel due to a pressure gradient or with the moving of the upper lid.The present analysis shows the effects of the fluid parameters on the velocity,the temperature,the entropy generation,and the Bejan number.The nonlinear boundary value problem of the flow problem is solved with the help of the regular perturbation method.To validate the perturbation solution,a numerical solution is also obtained with the help of the built-in command NDSolve of MATHEMATICA 11.0.The velocity profile shows the shear thickening behavior via first-order Eyring-Powell parameters.It is also observed that the profile of the Bejan number has a decreasing trend against the Brinkman number.Whenηi→0(i=1,2,3),the Eyring-Powell fluid is transformed into a Newtonian fluid.
基金Supported by University of Malaya under Grant No RG159/12AET.
文摘We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser(TDFL)using a newly devel-oped single-wall carbon nanotube-based saturable absorber.The TDFL generates the 25 th harmonic mode-locked stretched pulse train with a high repetition rate of 213MHz and a pulse duration of 710fs.The laser operates at 1901.6nm with an average power of 1.89mW,which corresponds to the pulse energy of 0.008nJ,at 1552nm pump power of 719mW.The peak-to-background ratio is measured to be 60dB,which indicates the stability of the laser.
基金the University of Malaya PPP under Grant No PV030/2012Athe University of Malaya Research Grant under Grant No RG144-12AET.
文摘We demonstrate a simple,compact and low-cost mode-locked erbium-doped fiber laser(EDFL)using a single-wall carbon nanotube(SWCNT)poly-ethylene oxide(PEO)composite as a passive saturable absorber(SA).The composite with an SWCNT concentration of 18wt%is prepared by mixing the SWCNT homogeneous solution with a diluted PEO polymer solution.A droplet of the polymer composite is applied on the fiber ferrule end,which is then mated to another clean ferrule connector to construct an SA.The SA is then integrated into the laser system to self-start stable mode locking at 1557 nm without employing a polarization controller.The EDFL generates a stable soliton pulse train with a duration of 0.81 ps,repetition rate of 44 MHz and average output power of 92.4μW at a 980 nm pump power of 26.8 mW.The soliton laser starts to lase at a pump power threshold of 14.6 mW.
基金Supported by University of Malaya PPP under Grant No PV029/2011B.
文摘We demonstrate a simple,compact and low cost Q-switched erbium-doped fiber laser(EDFL)using single-wall carbon nanotubes(CNTs)as a saturable absorber for possible applications in metrology,sensing,and medical diagnostics.The EDFL operates at around 1560 nm with repetition rates of 16.1 kHz and 6.4 kHz with saturable absorbers SA1 and SA2 at a pump power of 120 mW.The absorbers are constructed by optically driven deposition and normal deposition techniques.It is observed that the optical deposition method produces a Q-switched EDFL with a lower threshold of 70 mW and better Q-switching performance compared to that of the normal deposition method.The EDFL also has pulse energy of 90.3 nJ and pulse width of 11.6μs at 120 mW pump power.
文摘The thermal shock and fatigue behavior of pressureless sintered Al_(2)O_(3)-SiO_(2)-ZrO_(2)(ASZ)composites was studied.The influence of the thermal shock and fatigue on the strengthening response of ASZ has been investigated by measuring the strength retention and microstructural changes.The magnitude of the flexural strength and fracture of the ASZ has been compared with that of the monolithic Al_(2)O_(3)(A)and Al_(2)O_(3)-SiO_(2)-ZrO_(2)(AZ)composites under the same experimental conditions.Results indicated that the ASZ composites possess the highest resistance against thermal shock and fatigue,in comparison with A and AZ.The improvements were attributed to the enhancement in the fracture toughness of ASZ and the presence of multi-phase reinforcement.
基金financially supported by the Ministry of Education and the University of Malaya under Grant Nos.ER012-2013A and RP008D-13AET
文摘We propose a Q-switched Er-doped fiber laser （EDFL） with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol （PVA） thin film as a passive saturable absorber （SA）. The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 roW. At maximum 1480 nm pump power of 33.0 roW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56/as. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 roW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.
基金supported by Ministry of Higher Education under ERGS Grant scheme No.ER012-2012A
文摘A Q-switched ytterbium-doped fiber laser （YDFL） is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide （MWCNTs-PEO） film as a passive saturable absorber （SA）. The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation. The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW. The YDFL generates a stable pulse train with repetition rates ranging from 7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW. At 59.55-mW pump power, the lowest pulse width and the highest pulse energy are obtained at 12.18 μs and 143.5 n J, respectively.
基金supported by the University of Malaya Research Grant(UMRG)(Nos.RP008C-13AET and RU002/2013)
文摘We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber （TDF） laser, a homemade double-clad thulium-ytterbium co-doped fiber （TYDF） as the gain media, and a multi-walled carbon nanotube （MWCNT） based saturable absorber （SA）. We prepare the MWCNT composite by mixing a homogeneous solution of MWCNTs with a diluted polyvinyl alcohol （PVA） polymer solution and then drying it at room temperature to form a film. The film is placed between two fiber connectors as a SA before it is integrated into a laser ring cavity. The cavity consists of a 2 m long TDF pumped by a 800 nm laser diode and a 15 m long homemade TYDF pumped by a 905 nm multimode laser diode. A stable mode-locking pulse with a repetition rate of 34.6 MHz and a pulse width of 10.79 ps is obtained when the 905 nm multimode pump power reaches 1.8-2.2 W, while the single-mode 800 nm pump power is fixed at 141.5 mW at all times. To the best of our knowledge, this is the first reported mode-locked fiber laser using a MWCNT-based SA.
基金supported by Ministry of Higher Education (MOHE) under the Exploratory Research GrantScheme (ERGS) (No. ER012-2012A)the University of Malaya under a Pangurusan Penyelidikan Pascasiswazah (PPP) Grant (No. PV030/2012A)
文摘We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thulium- bismuth co-doped fiber （TBF） as a gain medium in conjunction with a carbon nanotube （CNT）-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 roW.
