37,161 research outputs found
Spin-lattice order in frustrated ZnCr2O4
Using synchrotron X-rays and neutron diffraction we disentangle spin-lattice
order in highly frustrated ZnCrO where magnetic chromium ions occupy
the vertices of regular tetrahedra. Upon cooling below 12.5 K the quandary of
anti-aligning spins surrounding the triangular faces of tetrahedra is resolved
by establishing weak interactions on each triangle through an intricate lattice
distortion. The resulting spin order is however, not simply a N\'{e}el state on
strong bonds. A complex co-planar spin structure indicates that antisymmetric
and/or further neighbor exchange interactions also play a role as ZnCrO
resolves conflicting magnetic interactions
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.AlāMgāSi 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 AlāMgāSi 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 AlāMgāSiāMnāFe and AlāMgāSiāFe 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 AlāMgāSiāMn 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 Ī±-AlFeMnSi phase with typical composition of Al24(Fe,Mn)6Si2. With increased Fe content, Ī²-AlFe was found in the microstructure with a long needle-shaped morphology, which was identified as Al13(Fe,Mn)4Si0.25. In the AlāMgāSi alloy, the identified Fe-rich intermetallics included the compact Ī±-AlFeSi phase with typical composition of Al8Fe2Si and the needle-shaped Ī²-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 Ī±-AlFeMnSi intermetallics and suppresses the formation of Ī²-AlFe phase in the AlāMgāSi 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.AlāMgāSi 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 AlāMgāSi 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 AlāMgāSiāMnāFe and AlāMgāSiāFe 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 AlāMgāSiāMn 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 Ī±-AlFeMnSi phase with typical composition of Al24(Fe,Mn)6Si2. With increased Fe content, Ī²-AlFe was found in the microstructure with a long needle-shaped morphology, which was identified as Al13(Fe,Mn)4Si0.25. In the AlāMgāSi alloy, the identified Fe-rich intermetallics included the compact Ī±-AlFeSi phase with typical composition of Al8Fe2Si and the needle-shaped Ī²-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 Ī±-AlFeMnSi intermetallics and suppresses the formation of Ī²-AlFe phase in the AlāMgāSi alloys, and thus improves their mechanical properties.EPSRC and JL
Leading Chiral Contributions to the Spin Structure of the Proton
The leading chiral contributions to the quark and gluon components of the
proton spin are calculated using heavy-baryon chiral perturbation theory.
Similar calculations are done for the moments of the generalized parton
distributions relevant to the quark and gluon angular momentum densities. These
results provide useful insight about the role of pions in the spin structure of
the nucleon, and can serve as a guidance for extrapolating lattice QCD
calculations at large quark masses to the chiral limit.Comment: 8 pages, 2 figures; a typo in Ref. 7 correcte
Instanton-inspired Model of QCD Phase Transition and Bubble Dynamics
We have reinvestigated the collision of gluonic bubbles in a SU(2) model of
QCD which was studied by Johnson, Choi and Kisslinger in the context of the
instanton-inspired model of QCD phase transition bubbles with plane wave
approximation. We discuss treacherous points of the instanton-inspired model
that cause the violation of causality due to the presence of imaginary gluon
fields. By constructing a new slightly modified Lorentzian model where we have
three independent real gluon fields, we reanalyzed the process of bubble
collisions. Our numerical results show some indication of forming a bubble wall
in colliding region.Comment: 19 pages, 32 figure
Melt superheating on the microstructure and mechanical properties of diecast Al-Mg-Si-Mn alloy
The application of aluminium alloys in automotive body structure is one of the main developments in recent years. The increase of the mechanical properties of the ductile die-casting is one of the most critical topics for the application. In this work, the effect of melt superheating on the morphology, size and distribution of Ī±-Al phase and Fe-rich intermetallics, and on the mechanical properties of the Al-Mg-Si-Mn diecast alloy was investigated. The results showed that the refined microstructure could be obtained through melt superheating. The volume fraction of dendritic Ī±-Al phase and the Fe-rich intermetallic phase formed in the shot sleeve was significantly reduced, resulting in the refined microstructure. Overall, the melt superheating could improve the mechanical properties of the yield strength, ultimate tensile strength, and elongation of the diecast Al-Mg-Si-Mn alloy. And, the Fe-rich intermetallic phase formed in the shot sleeve with the coarse compact morphology and formed in the die cavity with the fine compact particles were identified as the same Ī±-Al12(Fe,Mn)3Si composition in the present experimental conditions, which was not affected by the melt superheating.The financial support from Technology Strategy Board (TSB) under project No. 101172 is acknowledged. The authors also would like to thank the EPSRC (UK) and Jaguar Cars Ltd. (UK) for financial support under the grant for the EPSRC Centre - LiME
Spin dynamics and magnetic interactions of Mn dopants in the topological insulator BiTe
The magnetic and electronic properties of the magnetically doped topological
insulator BiMnTe were studied using electron spin
resonance (ESR) and measurements of static magnetization and electrical
transport. The investigated high quality single crystals of BiMnTe show a ferromagnetic phase transition for
at K. The Hall measurements reveal a p-type finite
charge-carrier density. Measurements of the temperature dependence of the ESR
signal of Mn dopants for different orientations of the external magnetic field
give evidence that the localized Mn moments interact with the mobile charge
carriers leading to a Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling
between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a
low-dimensional character of magnetic correlations that persist far above the
ferromagnetic ordering temperature
An optical fibre dynamic instrumented palpation sensor for the characterisation of biological tissue
AbstractThe diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre FabryāPĆ©rot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of Ā±0.4Ī¼m over a 721Ī¼m measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator
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