20,097 research outputs found
Effect of iron on the microstructure and mechanical property of Al-Mg-Si-Mn and Al-Mg-Si diecast alloys
This article is made available through the Brunel Open Access Publishing Fund. Copyright @ 2012 Elsevier B.V.This article has been made available through the Brunel Open Access Publishing Fund.AlâMgâSi based alloys can provide super ductility to satisfy the demands of thin wall castings in the application of automotive structure. In this work, the effect of iron on the microstructure and mechanical properties of the AlâMgâSi diecast alloys with different Mn concentrations is investigated. The CALPHAD (acronym of Calculation of Phase Diagrams) modelling with the thermodynamic properties of the multi-component AlâMgâSiâMnâFe and AlâMgâSiâFe systems is carried out to understand the role of alloying on the formation of different primary Fe-rich intermetallic compounds. The results showed that the Fe-rich intermetallic phases precipitate in two solidification stages in the high pressure die casting process: one is in the shot sleeve and the other is in the die cavity, resulting in the different morphologies and sizes. In the AlâMgâSiâMn alloys, the Fe-rich intermetallic phase formed in the shot sleeve exhibited coarse compact morphology and those formed in the die cavity were fine compact particles. Although with different morphologies, the compact intermetallics were identified as the same α-AlFeMnSi phase with typical composition of Al24(Fe,Mn)6Si2. With increased Fe content, ÎČ-AlFe was found in the microstructure with a long needle-shaped morphology, which was identified as Al13(Fe,Mn)4Si0.25. In the AlâMgâSi alloy, the identified Fe-rich intermetallics included the compact α-AlFeSi phase with typical composition of Al8Fe2Si and the needle-shaped ÎČ-AlFe phase with typical composition of Al13Fe4. Generally, the existence of iron in the alloy slightly increases the yield strength, but significantly reduces the elongation. The ultimate tensile strength maintains at similar levels when Fe contents is less than 0.5 wt%, but decreases significantly with the further increased Fe concentration in the alloys. CALPHAD modelling shows that the addition of Mn enlarges the Fe tolerance for the formation of α-AlFeMnSi intermetallics and suppresses the formation of ÎČ-AlFe phase in the AlâMgâSi alloys, and thus improves their mechanical properties.EPSRC and JL
Effect of iron on the microstructure and mechanical property of Al-Mg-Si-Mn and Al-Mg-Si diecast alloys
This article is made available through the Brunel Open Access Publishing Fund. Copyright @ 2012 Elsevier B.V.This article has been made available through the Brunel Open Access Publishing Fund.AlâMgâSi based alloys can provide super ductility to satisfy the demands of thin wall castings in the application of automotive structure. In this work, the effect of iron on the microstructure and mechanical properties of the AlâMgâSi diecast alloys with different Mn concentrations is investigated. The CALPHAD (acronym of Calculation of Phase Diagrams) modelling with the thermodynamic properties of the multi-component AlâMgâSiâMnâFe and AlâMgâSiâFe systems is carried out to understand the role of alloying on the formation of different primary Fe-rich intermetallic compounds. The results showed that the Fe-rich intermetallic phases precipitate in two solidification stages in the high pressure die casting process: one is in the shot sleeve and the other is in the die cavity, resulting in the different morphologies and sizes. In the AlâMgâSiâMn alloys, the Fe-rich intermetallic phase formed in the shot sleeve exhibited coarse compact morphology and those formed in the die cavity were fine compact particles. Although with different morphologies, the compact intermetallics were identified as the same α-AlFeMnSi phase with typical composition of Al24(Fe,Mn)6Si2. With increased Fe content, ÎČ-AlFe was found in the microstructure with a long needle-shaped morphology, which was identified as Al13(Fe,Mn)4Si0.25. In the AlâMgâSi alloy, the identified Fe-rich intermetallics included the compact α-AlFeSi phase with typical composition of Al8Fe2Si and the needle-shaped ÎČ-AlFe phase with typical composition of Al13Fe4. Generally, the existence of iron in the alloy slightly increases the yield strength, but significantly reduces the elongation. The ultimate tensile strength maintains at similar levels when Fe contents is less than 0.5 wt%, but decreases significantly with the further increased Fe concentration in the alloys. CALPHAD modelling shows that the addition of Mn enlarges the Fe tolerance for the formation of α-AlFeMnSi intermetallics and suppresses the formation of ÎČ-AlFe phase in the AlâMgâSi alloys, and thus improves their mechanical properties.EPSRC and JL
Investigation of the energy dependence of the orbital light curve in LS 5039
LS 5039 is so far the best studied -ray binary system at
multi-wavelength energies. A time resolved study of its spectral energy
distribution (SED) shows that above 1 keV its power output is changing along
its binary orbit as well as being a function of energy. To disentangle the
energy dependence of the power output as a function of orbital phase, we
investigated in detail the orbital light curves as derived with different
telescopes at different energy bands. We analysed the data from all existing
\textit{INTEGRAL}/IBIS/ISGRI observations of the source and generated the most
up-to-date orbital light curves at hard X-ray energies. In the -ray
band, we carried out orbital phase-resolved analysis of \textit{Fermi}-LAT data
between 30 MeV and 10 GeV in 5 different energy bands. We found that, at
100 MeV and 1 TeV the peak of the -ray emission is
near orbital phase 0.7, while between 100 MeV and 1 GeV it moves
close to orbital phase 1.0 in an orbital anti-clockwise manner. This result
suggests that the transition region in the SED at soft -rays (below a
hundred MeV) is related to the orbital phase interval of 0.5--1.0 but not to
the one of 0.0--0.5, when the compact object is "behind" its companion. Another
interesting result is that between 3 and 20 GeV no orbital modulation is found,
although \textit{Fermi}-LAT significantly (18) detects LS 5039.
This is consistent with the fact that at these energies, the contributions to
the overall emission from the inferior conjunction phase region (INFC, orbital
phase 0.45 to 0.9) and from the superior conjunction phase region (SUPC,
orbital phase 0.9 to 0.45) are equal in strength. At TeV energies the power
output is again dominant in the INFC region and the flux peak occurs at phase
0.7.Comment: 7 pages, 6 figures, accepted for publication in MNRA
On-Chip Matching Networks for Radio-Frequency Single-Electron-Transistors
In this letter, we describe operation of a radio-frequency superconducting
single electron transistor (RF-SSET) with an on-chip superconducting LC
matching network consisting of a spiral inductor L and its capacitance to
ground. The superconducting network has a lower parasitic capacitance and gives
a better matching for the RF-SSET than does a commercial chip inductor.
Moreover, the superconducting network has negligibly low dissipation, leading
to sensitive response to changes in the RF-SSET impedance. The charge
sensitivity 2.4*10^-6 e/(Hz)^1/2 in the sub-gap region and energy sensitivity
of 1.9 hbar indicate that the RF-SSET is operating in the vicinity of the shot
noise limit.Comment: 3 pages, 3 figures, REVTeX 4. To appear in Appl. Phys. Let
Analysis of RTN signals in Resistive-Switching RAM device and its correlation with device operations
Filament rupture/restoration induced by movement of defects, e.g. oxygen ions/vacancies, is considered as the switching mechanism in HfO2 RRAM. However, details of filament alteration during switching are still speculative, due to the limitations of existing experiment-based probing techniques, impeding its understanding. In this work, for the first time, an RTN-based defect tracking technique is developed for RRAM devices, which can monitor the movements of defects and statistically provide their spatial and energy profiles. The critical filament region is experimentally identified and its alteration is observed and correlated with switching operations under various operation conditions. This provides a useful tool for further development of RRAM technology
Exciton Valley Dynamics probed by Kerr Rotation in WSe2 Monolayers
We have experimentally studied the pump-probe Kerr rotation dynamics in
WSe monolayers. This yields a direct measurement of the exciton valley
depolarization time . At T=4K, we find ps, a fast
relaxation time resulting from the strong electron-hole Coulomb exchange
interaction in bright excitons. The exciton valley depolarization time
decreases significantly when the lattice temperature increases with
being as short as 1.5ps at 125K. The temperature dependence is well explained
by the developed theory taking into account the exchange interaction and a fast
exciton scattering time on short-range potentials.Comment: 5 pages, 3 figure
A PN-type quantum barrier for InGaN/GaN light emitting diodes
Cataloged from PDF version of article.In this work, InGaN/GaN light-emitting diodes (LEDs) with PN-type quantum barriers are comparatively studied both theoretically and experimentally. A strong enhancement in the optical output power is obtained from the proposed device. The improved performance is attributed to the screening of the quantum confined Stark effect (QCSE) in the quantum wells and improved hole transport across the active region. In addition, the enhanced overall radiative recombination rates in the multiple quantum wells and increased effective energy barrier height in the conduction band has substantially suppressed the electron leakage from the active region. Furthermore, the electrical conductivity in the proposed devices is improved. The numerical and experimental results are in excellent agreement and indicate that the PN-type quantum barriers hold great promise for high-performance InGaN/GaN LEDs. (C) 2013 Optical Society of Americ
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