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381.
Modelling and validation: Casting of Al and TiAl alloys in gravity and centrifugal casting processes
N.J. Humphreys D. McBride D.M. Shevchenko T.N. Croft P. Withey N.R. Green M. Cross 《Applied Mathematical Modelling》2013,37(14-15):7633-7643
Components which best utilise the properties of high temperature titanium alloys are characterised by thin sections of a few millimetres thickness and hundreds of millimetres length. These alloys however are difficult to work with, being highly reactive in a molten state, necessitating a low superheat during processing. Centrifugal casting is therefore utilised as a candidate production method, as under the centrifugal force, metal can rapidly fill thicknesses substantially less than a millimetre before it solidifies. However, due to the high liquid metal velocity developed there is a high risk of turbulent flow and of the trapping of any gas present within the liquid metal.This challenging application involves a combination of complex rotating geometries, significant centrifugal forces and high velocity transient free surface flows, coupled with simultaneous heat transfer and solidification. Capturing these interacting physical phenomena, free surface flows, trapped air and associated defects is a complex modelling task.Building upon earlier work on computational modelling the authors have previously described to capture and validate the fluid dynamics behaviour of rotating systems, this contribution considers the modelling and validation of such systems to capture the coupled flow and thermal solidification behaviour and associated defect development.A bench-mark test case is employed to validate the effect of solidification on the fluidity of an aluminium alloy. Validation is also performed against a series of casting experiments to establish the models ability to capture the filling process and predict defects due to air entrapment within the solidified metal. 相似文献
382.
Valerie Cross Xinran Yu Xueheng Hu 《International Journal of Approximate Reasoning》2013,54(7):861-875
This paper theoretically and empirically investigates ontological similarity. Tversky’s parameterized ratio model of similarity [3] is shown as a unifying basis for many of the well-known ontological similarity measures. A new family of ontological similarity measures is proposed that allows parameterizing the characteristic set used to represent an ontological concept. The three subontologies of the prominent Gene Ontology (GO) are used in an empirical investigation of several ontological similarity measures. Another study using well known semantic similarity within two different anatomy ontologies, the NCIT anatomy and the mouse anatomy, is also presented for comparison to several of the GO results. A discussion of the correlation among the measures is presented as well as a comparison of the effects of two different methods of determining a concept’s information content, corpus-based and ontology-based. 相似文献
383.
384.
Murray DT Lu Y Cross TA Quine JR 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,210(1):82-89
Residual dipolar couplings between spin-1/2 and quadrupolar nuclei are often observed and exploited in the magic-angle spinning (MAS) NMR spectra of spin-1/2 nuclei. These orientation-dependent splittings contain information on the dipolar interaction, which can be translated into structural information. The same type of splittings may also be observed for pairs of quadrupolar nuclei, although information is often difficult to extract from the quadrupolar-broadened lineshapes. Here, the complete theory for describing the dipolar coupling between two quadrupolar nuclei in the frequency domain by Hamiltonian diagonalization is given. The theory is developed under MAS and double-rotation (DOR) conditions, and is valid for any spin quantum numbers, quadrupolar coupling constants, asymmetry parameters, and tensor orientations at both nuclei. All terms in the dipolar Hamiltonian become partially secular and contribute to the NMR spectrum. The theory is validated using experimental 11B and 35/37Cl NMR experiments carried out on powdered B-chlorocatecholborane, where both MAS and DOR are used to help separate effects of the quadrupolar interaction from those of the dipolar interaction. It is shown that the lineshapes are sensitive to the quadrupolar coupling constant of both nuclei and to the J coupling (including its sign). From these experiments, the dipolar coupling constant for a heteronuclear spin pair of quadrupolar nuclei may be obtained as well as the sign of the quadrupolar coupling constant of the perturbing nucleus; these are two parameters that are difficult to obtain experimentally otherwise. 相似文献
385.
O. E. Scott-Emuakpor T. J. George C. J. Cross M.-H. H. Shen 《Experimental Mechanics》2011,51(8):1317-1323
The dissipation of strain energy density per cycle was analyzed to understand its trend through a fatigue process. The motivation
behind this analysis is to improve a fatigue life prediction method, which is based on a strain energy and failure correlation.
The correlation states that the same amount of strain energy is dissipated during both monotonic fracture and cyclic fatigue.
This means the summation of strain energy density per cycle is equal to the total strain energy density dissipated monotonically.
In order to validate this understanding, the strain energy density per cycle was analyzed at several alternating stress levels
for fatigue life of Aluminum 6061-T6 (Al 6061-T6) between 103 and 105 cycles. The analysis includes the following: Alternating between high and low operating frequencies (50x magnitude difference),
interruption of cyclic load during testing, and idle/zero-loading intervals of 20–40 minutes in-between cyclic loading sequences.
All experimental results show a consistent trend of cyclic softening as the loading cycles approach failure; however, due
to an inefficient curve fit procedure of the stress-dependent strain equation at low alternating stresses onto the experimental
stress-strain data, a new approach for calculating the strain energy density per cycle is explored and shows promising results. 相似文献
386.
Finlay P Ettenauer S Ball GC Leslie JR Svensson CE Andreoiu C Austin RA Bandyopadhyay D Cross DS Demand G Djongolov M Garrett PE Green KL Grinyer GF Hackman G Leach KG Pearson CJ Phillips AA Sumithrarachchi CS Triambak S Williams SJ 《Physical review letters》2011,106(3):032501
A high-precision half-life measurement for the superallowed β+ emitter 26Al(m) was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1/2 6346.54 ± 0.46(stat) ± 0.60 (syst) ms, consistent with, but 2.5 times more precise than, the previous world average. The 26Al(m) half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed β decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for (26)Al(m), 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi β-decay studies used to test the conserved vector current hypothesis and determine the V(ud) element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. 相似文献
387.
Edward D. Cross Kristen L. MacDonald Robert McDonald Matthias Bierenstiel 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(1):23-27
The reaction of dichlorido(cod)palladium(II) (cod = 1,5‐cyclooctadiene) with 2‐(benzylsulfanyl)aniline followed by heating in N,N‐dimethylformamide (DMF) produces the linear trinuclear Pd3 complex bis(μ2‐1,3‐benzothiazole‐2‐thiolato)bis[μ2‐2‐(benzylsulfanyl)anilinido]dichloridotripalladium(II) N,N‐dimethylformamide disolvate, [Pd3(C7H4NS2)2(C13H12NS)2Cl2]·2C3H7NO. The molecule has symmetry and a Pd...Pd separation of 3.2012 (4) Å. The outer PdII atoms have a square‐planar geometry formed by an N,S‐chelating 2‐(benzylsulfanyl)anilinide ligand, a chloride ligand and the thiolate S atom of a bridging 1,3‐benzothiazole‐2‐thiolate ligand, while the central PdII core shows an all N‐coordinated square‐planar geometry. The geometry is perfectly planar within the PdN4 core and the N—Pd—N bond angles differ significantly [84.72 (15)° for the N atoms of ligands coordinated to the same outer Pd atom and 95.28 (15)° for the N atoms of ligands coordinated to different outer Pd atoms]. This trinuclear Pd3 complex is the first example of one in which 1,3‐benzothiazole‐2‐thiolate ligands are only N‐coordinated to one Pd centre. The 1,3‐benzothiazole‐2‐thiolate ligands were formed in situ from 2‐(benzylsulfanyl)aniline. 相似文献
388.
Fister TT Seidler GT Shirley EL Vila FD Rehr JJ Nagle KP Linehan JC Cross JO 《The Journal of chemical physics》2008,129(4):044702
New theoretical and experimental investigations of the occupied and unoccupied local electronic densities of states (DOS) are reported for alpha-Li(3)N. Band-structure and density-functional theory calculations confirm the absence of covalent bonding character. However, real-space full-multiple-scattering (RSFMS) calculations of the occupied local DOS find less extreme nominal valences than have previously been proposed. Nonresonant inelastic x-ray scattering, RSFMS calculations, and calculations based on the Bethe-Salpeter equation are used to characterize the unoccupied electronic final states local to both the Li and N sites. There is a good agreement between experiment and theory. Throughout the Li 1s near-edge region, both experiment and theory find strong similarities in the s-and p-type components of the unoccupied local final DOS projected onto an orbital angular momentum basis (l-DOS). An unexpected, significant correspondence exists between the near-edge spectra for the Li 1s and N 1s initial states. We argue that both spectra are sampling essentially the same final DOS due to the combination of long core-hole lifetimes, long photoelectron lifetimes, and the fact that orbital angular momentum is the same for all relevant initial states. Such considerations may be generally applicable for low atomic number compounds. 相似文献
389.
A secondary gate as a mechanism for inhibition of the M2 proton channel by amantadine 总被引:1,自引:0,他引:1
The mechanism of inhibition of the influenza A virus M2 proton channel by the antiviral drug amantadine has been under intense investigation. The importance of a mechanistic understanding is heightened by the prevalence of amantadine-resistant mutations. To gain mechanistic insight at the molecular level, we carried out extensive molecular dynamics simulations of the tetrameric M2 proton channel in both apo and amantadine-bound forms in a lipid bilayer. The simulation of the apo form revealed that Val27 from the four M2 subunits can form a secondary gate near the channel entrance and break the water wire in the channel pore. This gate arises from physical occlusion and the elimination of hydrogen-bonding partners for water molecules. In the presence of amantadine, the secondary gate formed by Val27 and the drug molecule lying just below form an extended blockage, which breaks the water wire throughout the simulation. The location and orientation of amantadine inside of the channel pore as found in our simulation are supported by a host of experimental observations. Our study suggests a novel role for Val27 in the inhibition of the M2 proton channel by amantadine. 相似文献
390.
Can TV Sharma M Hung I Gor'kov PL Brey WW Cross TA 《Journal of the American Chemical Society》2012,134(22):9022-9025
As a small tetrameric helical membrane protein, the M2 proton channel structure is highly sensitive to its environment. As a result, structural data from a lipid bilayer environment have proven to be essential for describing the conductance mechanism. While oriented sample solid-state NMR has provided a high-resolution backbone structure in lipid bilayers, quaternary packing of the helices and many of the side-chain conformations have been poorly restrained. Furthermore, the quaternary structural stability has remained a mystery. Here, the isotropic chemical shift data and interhelical cross peaks from magic angle spinning solid-state NMR of a liposomal preparation strongly support the quaternary structure of the transmembrane helical bundle as a dimer-of-dimers structure. The data also explain how the tetrameric stability is enhanced once two charges are absorbed by the His37 tetrad prior to activation of this proton channel. The combination of these two solid-state NMR techniques appears to be a powerful approach for characterizing helical membrane protein structure. 相似文献