In this work,phase and morphology-tuned MoO_(3) nanostructures are synthesized through a novel modified co-precipitation method,and their electrochemical properties are investigated.For the first time,such a simple su...In this work,phase and morphology-tuned MoO_(3) nanostructures are synthesized through a novel modified co-precipitation method,and their electrochemical properties are investigated.For the first time,such a simple surfactant-assisted synthesis process aided by minor temperature variations is reported which results in phase transition of the nanoparticles from h-MoO_(3) nano-rods to a-MoO_(3) nano-flakes.The nanostructures thus developed are highly porous and crystalline with significantly large specific surface area as compared to previous literature.The theoretical bandgap energy of the optimized sample calculated using Perdew-Zunger local density approximation(LDA) is in good agreement with the experimental findings.An overall structural,morphological,and surface-behavioural analysis predicts the electrochemical superiority in 2D a-MoO_(3).The cyclic voltammetry and galvano-potentiometry measurements of 2D a-MoO_(3) in the potential window of-0.6 V to +0.2 V present the highest pseudosupercapacitive response with a maximum specific capacitance of 829 F g^(-1)at 2 A g^(-1)as compared to h-MoO_(3) (452 F g^(-1)) and h@a-MoO_(3) (783 F g^(-1)).Thus,the MoO_(3) 2D nanostructures synthesized through our novel synthesis technique display excellent specific capacitance as compared to previous reported data.Additionally,a-MoO_(3) exhibits a galvanostatic charging-discharging cyclic stability of about 91%after 2000 cycles,indicating that it can serve as an excellent electrode material for supercapacitors.A solid-state asymmetric supercapacitor device is successfully constructed using a-MoO_(3) which can light up 4 red LEDs for 10 s.The specific energy density of the device reaches a maximum value of 36.3 W h kg^(-1)at the power density of 50 W kg^(-1).展开更多
The corrosion behavior of Mg,AZ31 and AZ91 has been evaluated in 3.5%NaCl solution using weight loss,electrochemical polarization and impedance measurements.Corrosion rate derived from the weight losses demonstrated t...The corrosion behavior of Mg,AZ31 and AZ91 has been evaluated in 3.5%NaCl solution using weight loss,electrochemical polarization and impedance measurements.Corrosion rate derived from the weight losses demonstrated the occurrence of steeply fast corrosion reaction on AZ91 alloy after three hours of immersion,indicating the start of galvanic corrosion.An increase of corrosion rate with immersion time was also observed for AZ31 but with lesser extent than AZ91 alloy.Whereas Mg metals showed a decrease of corrosion rate with immersion time,suggesting the formation of a protective layer on their surfaces.In contrast,the corrosion current density(I_(corr))derived from the Tafel plots,exhibited their corrosion resistances in order of Mg>AZ91>AZ31.Electrochemical charge transfer resistance(R_(ct))and double layer capacitance measured by electrochemical impedance spectroscopy(EIS),are well in accordance with the measured I_(corr).EIS measurements with time and microstructural examination of the corroded and uncorroded samples are helpful in elucidation of results measured by electrochemical polarization.展开更多
The unsteady laminar magnetohydrodynamics （MHD） boundary layer flow and heat transfer of nanofluids over an accelerating convectively heated stretching sheet are numerically studied in the presence of a transverse m...The unsteady laminar magnetohydrodynamics （MHD） boundary layer flow and heat transfer of nanofluids over an accelerating convectively heated stretching sheet are numerically studied in the presence of a transverse magnetic field with heat source/sink The unsteady governing equations are solved by a shooting method with the Runge-Kutta- Fehlberg scheme. Three different types of water based nanofluids, containing copper, aluminium oxide, and titanium dioxide, are taken into consideration. The effects of the pertinent parameters on the fluid velocity, the temperature, the entropy generation num- ber, the Bejan number, the shear stress, and the heat transfer rate at the sheet surface are graphically and quantitatively discussed in detail. A comparison of the entropy generation due to the heat transfer and the fluid friction is made with the help of the Bejan number. It is observed that the presence of the metallic nanoparticles creates more entropy in the nanofluid flow than in the regular fluid flow.展开更多
An aluminium alloy and its composite with dispersed SiC particles made by liquid metallurgy route were extruded under optimized conditions.The properties were characterized in terms of microstructure,hardness and slid...An aluminium alloy and its composite with dispersed SiC particles made by liquid metallurgy route were extruded under optimized conditions.The properties were characterized in terms of microstructure,hardness and sliding wear behaviour and then compared between the extruded and cast alloys and composites,in order to understand the benefits of composite and extrusion on the alloy.It was observed that composites drastically increased the hardness and the extruded composites further increased this value.The advantage of composites was realized in sliding wear tests.展开更多
We present an all-fiber dual-wavelength holmium-doped veloped holmium-doped fiber （HDF） as a gain medium fiber laser operating in 2 #m region using a newly de- The proposed fiber laser is constructed by using a hybr...We present an all-fiber dual-wavelength holmium-doped veloped holmium-doped fiber （HDF） as a gain medium fiber laser operating in 2 #m region using a newly de- The proposed fiber laser is constructed by using a hybrid gain medium, i.e., a thulium ytterbium co-doped fiber （TYDF） and an HDF in conjunction with a simple half-opened linear cavity, which is formed by a broadband mirror and an output coupler reflector. Without the HDF, the TYDF laser operates at wavelengths of 1991 and 1999nm with a signal-to-noise ratio of more than 34dB and the slope efficiency of 26.16 %. With the HDF, dual-wavelength output lines are obtained at 2075 and 2083nm with signal-to-noise ratios of more than difference between the two peaks of less than 1 dB at 17dB, 3dB bandwidth of less than 0.2nm and the power the TYDF laser pump power of 320roW.展开更多
We demonstrate the generation of dark and bright solitons with our homemade zirconia-based erbium-doped fiber and graphene oxide（GO） saturable absorber in anomalous dispersion region.The GO is fabricated using an ab...We demonstrate the generation of dark and bright solitons with our homemade zirconia-based erbium-doped fiber and graphene oxide（GO） saturable absorber in anomalous dispersion region.The GO is fabricated using an abridged Hummer＇s method,which is combined with polyethylene oxide to produce a composite film.The film is sandwiched between two optical ferrules and embedded in the laser cavity to enhance its birefringence and nonlinearity.The self-starting bright soliton is easily generated at pump power of 78 mW with the whole length cavity of 14.7 m.The laser produces the bright pulse train with repetition rate,pulse width,pulse energy and central wavelength being 13.9 MHz,0.6 ps,2.74 p J and 1577.46 nm,respectively.Then,by adding the 10 m of single mode fiber into the laser cavity,dark soliton pulse is produced.For the formation of dark pulse train,the measured repetition rate,pulse width,pulse energy and central wavelength are 8.3 MHz,20 ns and 4.98 p J and1596.82 nm,respectively.Both pulses operate in the anomalous region.展开更多
We demonstrate an efficient fiber laser operating at 1901.6 nm using a newly developed thulium bismuth co-doped fiber(TBF)with dual pumping at 792 nm and 1552 nm.The fiber was fabricated using modified chemical vapor ...We demonstrate an efficient fiber laser operating at 1901.6 nm using a newly developed thulium bismuth co-doped fiber(TBF)with dual pumping at 792 nm and 1552 nm.The fiber was fabricated using modified chemical vapor deposition and solution doping processes.The dopant concentrations(wt%)and compositions inside the core are 0.15 Bi_(2)O_(3),0.3 Tm_(2)O_(3),1.0 Al_(2)O_(3) and 12.0 GeO_(2).The TBF laser operates at 1901.6 nm with a lasing efficiency of 33.2%and pump power threshold of 85 mW using a 2-m-long TBF in a linear cavity with two fiber Bragg gratings(FBGs).The high efficiency is attributed to the use of additional 1552 nm pump to complement 792 nm pumping.The maximum output power of 225 mW is achieved at the pump power of 820 mW with the optimum length of 2 m.展开更多
An efficient and compact double-pass optical fiber amplifier is demonstrated using a newly developed hafnia bismuth erbium co-doped fiber（HBEDF） as a gain medium. The HBEDF is fabricated using a modified chemical va...An efficient and compact double-pass optical fiber amplifier is demonstrated using a newly developed hafnia bismuth erbium co-doped fiber（HBEDF） as a gain medium. The HBEDF is fabricated using a modified chemical vapor deposition in conjunction with solution doping. The fiber has an erbium ion concentration of 12500 ppm.At the optimum length of 0.5 m, the HBEDF amplifier（HBEDFA） achieves a flat gain of 26 d B with a gain variation of less than 1.5 d B within a wavelength region from 1530 to 1560 nm when the input signal and pump power are fixed at-30 d Bm and 140 m W, respectively. On the other hand, at the input signal power of-10 d Bm,the HBEDFA also achieves a flat gain of 14.2 d B with a gain variation of less than 2.5 d B within a wide wavelength region from 1525 to 1570 nm. Compared with the conventional zirconia erbium co-doped fiber based amplifier,the proposed HBEDFA obtains a more efficient gain and lower noise figure. For an input signal of-30 d Bm, the gain improvements of 6.2 d B and 4.8 d B are obtained at 1525 nm and 1540 nm, respectively.展开更多
Ising superconductivity,observed in NbSe2 and similar materials,has generated tremendous interest.Recently,attention was called to the possible role that spin fluctuations(SF)play in this phenomenon,in addition to the...Ising superconductivity,observed in NbSe2 and similar materials,has generated tremendous interest.Recently,attention was called to the possible role that spin fluctuations(SF)play in this phenomenon,in addition to the dominant electron–phonon coupling(EPC);the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet Leggett oscillations.However,these hypotheses have not been put to a quantitative test.In this paper,we report first principle calculations of the EPC and also estimate coupling with SF,including full momentum dependence.We find that:(1)EPC is strongly anisotropic,largely coming from the K-K0 scattering,and therefore excludes triplet symmetry even as an excited state;(2)superconductivity is substantially weakened by SF,but anisotropy remains as above;and,(3)we do find the possibility of a Leggett mode,not in a singlet–triplet but in an s_(++)–s_(±)channel.展开更多
The electrical characterization of AlGaN/GaN interface is reported.The dependence of two-dimensional electron gas（2-DEG） density at the interface on the Al mole fraction and thickness of AIGaN layer as well as on th...The electrical characterization of AlGaN/GaN interface is reported.The dependence of two-dimensional electron gas（2-DEG） density at the interface on the Al mole fraction and thickness of AIGaN layer as well as on the thickness of GaN cap layer is presented.This information can be used to design and fabricate AlGaN/GaN based MODFET（modulation doped field effect transistor） for optimum DC and RF characteristics.展开更多
文摘In this work,phase and morphology-tuned MoO_(3) nanostructures are synthesized through a novel modified co-precipitation method,and their electrochemical properties are investigated.For the first time,such a simple surfactant-assisted synthesis process aided by minor temperature variations is reported which results in phase transition of the nanoparticles from h-MoO_(3) nano-rods to a-MoO_(3) nano-flakes.The nanostructures thus developed are highly porous and crystalline with significantly large specific surface area as compared to previous literature.The theoretical bandgap energy of the optimized sample calculated using Perdew-Zunger local density approximation(LDA) is in good agreement with the experimental findings.An overall structural,morphological,and surface-behavioural analysis predicts the electrochemical superiority in 2D a-MoO_(3).The cyclic voltammetry and galvano-potentiometry measurements of 2D a-MoO_(3) in the potential window of-0.6 V to +0.2 V present the highest pseudosupercapacitive response with a maximum specific capacitance of 829 F g^(-1)at 2 A g^(-1)as compared to h-MoO_(3) (452 F g^(-1)) and h@a-MoO_(3) (783 F g^(-1)).Thus,the MoO_(3) 2D nanostructures synthesized through our novel synthesis technique display excellent specific capacitance as compared to previous reported data.Additionally,a-MoO_(3) exhibits a galvanostatic charging-discharging cyclic stability of about 91%after 2000 cycles,indicating that it can serve as an excellent electrode material for supercapacitors.A solid-state asymmetric supercapacitor device is successfully constructed using a-MoO_(3) which can light up 4 red LEDs for 10 s.The specific energy density of the device reaches a maximum value of 36.3 W h kg^(-1)at the power density of 50 W kg^(-1).
文摘The corrosion behavior of Mg,AZ31 and AZ91 has been evaluated in 3.5%NaCl solution using weight loss,electrochemical polarization and impedance measurements.Corrosion rate derived from the weight losses demonstrated the occurrence of steeply fast corrosion reaction on AZ91 alloy after three hours of immersion,indicating the start of galvanic corrosion.An increase of corrosion rate with immersion time was also observed for AZ31 but with lesser extent than AZ91 alloy.Whereas Mg metals showed a decrease of corrosion rate with immersion time,suggesting the formation of a protective layer on their surfaces.In contrast,the corrosion current density(I_(corr))derived from the Tafel plots,exhibited their corrosion resistances in order of Mg>AZ91>AZ31.Electrochemical charge transfer resistance(R_(ct))and double layer capacitance measured by electrochemical impedance spectroscopy(EIS),are well in accordance with the measured I_(corr).EIS measurements with time and microstructural examination of the corroded and uncorroded samples are helpful in elucidation of results measured by electrochemical polarization.
文摘The unsteady laminar magnetohydrodynamics （MHD） boundary layer flow and heat transfer of nanofluids over an accelerating convectively heated stretching sheet are numerically studied in the presence of a transverse magnetic field with heat source/sink The unsteady governing equations are solved by a shooting method with the Runge-Kutta- Fehlberg scheme. Three different types of water based nanofluids, containing copper, aluminium oxide, and titanium dioxide, are taken into consideration. The effects of the pertinent parameters on the fluid velocity, the temperature, the entropy generation num- ber, the Bejan number, the shear stress, and the heat transfer rate at the sheet surface are graphically and quantitatively discussed in detail. A comparison of the entropy generation due to the heat transfer and the fluid friction is made with the help of the Bejan number. It is observed that the presence of the metallic nanoparticles creates more entropy in the nanofluid flow than in the regular fluid flow.
文摘An aluminium alloy and its composite with dispersed SiC particles made by liquid metallurgy route were extruded under optimized conditions.The properties were characterized in terms of microstructure,hardness and sliding wear behaviour and then compared between the extruded and cast alloys and composites,in order to understand the benefits of composite and extrusion on the alloy.It was observed that composites drastically increased the hardness and the extruded composites further increased this value.The advantage of composites was realized in sliding wear tests.
基金Supported by the University of Malaya under Grant No PG175-2015B
文摘We present an all-fiber dual-wavelength holmium-doped veloped holmium-doped fiber （HDF） as a gain medium fiber laser operating in 2 #m region using a newly de- The proposed fiber laser is constructed by using a hybrid gain medium, i.e., a thulium ytterbium co-doped fiber （TYDF） and an HDF in conjunction with a simple half-opened linear cavity, which is formed by a broadband mirror and an output coupler reflector. Without the HDF, the TYDF laser operates at wavelengths of 1991 and 1999nm with a signal-to-noise ratio of more than 34dB and the slope efficiency of 26.16 %. With the HDF, dual-wavelength output lines are obtained at 2075 and 2083nm with signal-to-noise ratios of more than difference between the two peaks of less than 1 dB at 17dB, 3dB bandwidth of less than 0.2nm and the power the TYDF laser pump power of 320roW.
文摘We demonstrate the generation of dark and bright solitons with our homemade zirconia-based erbium-doped fiber and graphene oxide（GO） saturable absorber in anomalous dispersion region.The GO is fabricated using an abridged Hummer＇s method,which is combined with polyethylene oxide to produce a composite film.The film is sandwiched between two optical ferrules and embedded in the laser cavity to enhance its birefringence and nonlinearity.The self-starting bright soliton is easily generated at pump power of 78 mW with the whole length cavity of 14.7 m.The laser produces the bright pulse train with repetition rate,pulse width,pulse energy and central wavelength being 13.9 MHz,0.6 ps,2.74 p J and 1577.46 nm,respectively.Then,by adding the 10 m of single mode fiber into the laser cavity,dark soliton pulse is produced.For the formation of dark pulse train,the measured repetition rate,pulse width,pulse energy and central wavelength are 8.3 MHz,20 ns and 4.98 p J and1596.82 nm,respectively.Both pulses operate in the anomalous region.
基金Supported by the University of Malaya PPP under Grant No PV033/2011B,the Department of Science and Technology of the Government of India,the Director and the Staff Members of the Central Glass and Ceramic Research Institute(CGCRI),the Council of Scientific and Industrial Research,India,for awarding a CSIR-research fellowship,and the University of Malaya under the HIR Grant No D000009-16001.
文摘We demonstrate an efficient fiber laser operating at 1901.6 nm using a newly developed thulium bismuth co-doped fiber(TBF)with dual pumping at 792 nm and 1552 nm.The fiber was fabricated using modified chemical vapor deposition and solution doping processes.The dopant concentrations(wt%)and compositions inside the core are 0.15 Bi_(2)O_(3),0.3 Tm_(2)O_(3),1.0 Al_(2)O_(3) and 12.0 GeO_(2).The TBF laser operates at 1901.6 nm with a lasing efficiency of 33.2%and pump power threshold of 85 mW using a 2-m-long TBF in a linear cavity with two fiber Bragg gratings(FBGs).The high efficiency is attributed to the use of additional 1552 nm pump to complement 792 nm pumping.The maximum output power of 225 mW is achieved at the pump power of 820 mW with the optimum length of 2 m.
文摘An efficient and compact double-pass optical fiber amplifier is demonstrated using a newly developed hafnia bismuth erbium co-doped fiber（HBEDF） as a gain medium. The HBEDF is fabricated using a modified chemical vapor deposition in conjunction with solution doping. The fiber has an erbium ion concentration of 12500 ppm.At the optimum length of 0.5 m, the HBEDF amplifier（HBEDFA） achieves a flat gain of 26 d B with a gain variation of less than 1.5 d B within a wavelength region from 1530 to 1560 nm when the input signal and pump power are fixed at-30 d Bm and 140 m W, respectively. On the other hand, at the input signal power of-10 d Bm,the HBEDFA also achieves a flat gain of 14.2 d B with a gain variation of less than 2.5 d B within a wide wavelength region from 1525 to 1570 nm. Compared with the conventional zirconia erbium co-doped fiber based amplifier,the proposed HBEDFA obtains a more efficient gain and lower noise figure. For an input signal of-30 d Bm, the gain improvements of 6.2 d B and 4.8 d B are obtained at 1525 nm and 1540 nm, respectively.
基金The work at GMU(S.D.and I.I.M.)was supported by Office of Naval Research through grant N00014-20-1-2345H.P.and E.R.M.acknowledge support from the National Science Foundation(NSF)under Grant No.DMR-2035518 and Grant No.OAC-2103991 for method development,superconductivity analysis,and code develop-ment.D.F.A+2 种基金was supported by the U.S.Department of Energy,Office of Basic Energy Sciences,Division of Materials Sciences and Engineering,under Award No.DE-SC0021971This work used the Extreme Science and Engineering Discovery Environment(XSEDE)70 which is supported by NSF Award No.ACI-1548562Specifically,this work used Comet at the San Diego Supercomputer Center through allocation TG-DMR180071.
文摘Ising superconductivity,observed in NbSe2 and similar materials,has generated tremendous interest.Recently,attention was called to the possible role that spin fluctuations(SF)play in this phenomenon,in addition to the dominant electron–phonon coupling(EPC);the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet Leggett oscillations.However,these hypotheses have not been put to a quantitative test.In this paper,we report first principle calculations of the EPC and also estimate coupling with SF,including full momentum dependence.We find that:(1)EPC is strongly anisotropic,largely coming from the K-K0 scattering,and therefore excludes triplet symmetry even as an excited state;(2)superconductivity is substantially weakened by SF,but anisotropy remains as above;and,(3)we do find the possibility of a Leggett mode,not in a singlet–triplet but in an s_(++)–s_(±)channel.
文摘The electrical characterization of AlGaN/GaN interface is reported.The dependence of two-dimensional electron gas（2-DEG） density at the interface on the Al mole fraction and thickness of AIGaN layer as well as on the thickness of GaN cap layer is presented.This information can be used to design and fabricate AlGaN/GaN based MODFET（modulation doped field effect transistor） for optimum DC and RF characteristics.
