The realization of light weight design of components with local, load adapted properties is a major goal in the development of new manufacturing and processing methods of metal composite materials. A ...main challenge in the manufacturing of compounds by forming consists in the realization of the necessary conditions for the initiation of the diffusion process and the generation of metallic bonding. A combination of high contact tensions with specific forming conditions such as temperature distribution and surface enlargement is required in order to initiate the diffusion of atoms during the forming process. The article presents FEM-simulation and investigation of contact and forming conditions of aluminum-magnesium composites with respect to an incremental forming method. The characteristics of the compound materials, surface enlargement and local forming conditions as well as temperature gradients are important factors for the diffusion processes. The investigation of contact conditions during compound formation is a prerequisite for the further design of forming methods and the base for new approaches of generating composites of two light metal alloys into products with favorable properties such as high specific strength and corrosion resistance.
Quark orbital angular momentum in the proton is evaluated via a Lattice QCD calculation of the second Mellin moment of the twist-3 generalized parton distribution \(\widetilde{E}_{2T} \) in the ...forward limit. The connection between this approach to quark orbital angular momentum and approaches previously utilized in Lattice QCD calculations, via generalized transverse momentum-dependent parton distributions and via Ji's sum rule, is reviewed. This connection can be given in terms of Lorentz invariance and equation of motion relations. The calculation of the second Mellin moment of \(\widetilde{E}_{2T} \) proceeds via a finite-momentum proton matrix element of a quark bilocal operator with a straight-line gauge connection and separation in both the longitudinal and transverse directions. The dependence on the former component serves to extract the second Mellin moment, whereas the dependence on the latter component provides a transverse momentum cutoff for the matrix element. Furthermore, a derivative of the matrix element with respect to momentum transfer in the forward limit is required, which is obtained using a direct derivative method. The calculation utilizes a clover fermion ensemble at pion mass 317 MeV. The resulting quark orbital angular momentum is consistent with previous evaluations through alternative approaches, albeit with greater statistical uncertainty using a comparable number of samples.
Previous Lattice QCD calculations of nucleon transverse momentum-dependent parton distributions (TMDs) focused on the case of transversely polarized nucleons, and thus did not encompass two ...leading-twist TMDs associated with longitudinal polarization, namely, the helicity TMD and the worm-gear TMD corresponding to transversely polarized quarks in a longitudinally polarized nucleon. Based on a definition of TMDs via hadronic matrix elements of quark bilocal operators containing staple-shaped gauge connections, TMD observables characterizing the aforementioned two TMDs are evaluated, utilizing an RBC/UKQCD domain wall fermion ensemble at the physical pion mass.
A Lattice QCD approach to quark orbital angular momentum in the proton based on generalized transverse momentum-dependent parton distributions (GTMDs) is enhanced methodologically by incorporating a ...direct derivative technique. This improvement removes a significant numerical bias that had been seen to afflict results of a previous study. In particular, the value obtained for Ji quark orbital angular momentum is reconciled with the one obtained independently via Ji's sum rule, validating the GMTD approach. Since GTMDs simultaneously contain information about the quark impact parameter and transverse momentum, they permit a direct evaluation of the cross product of the latter. They are defined through proton matrix elements of a quark bilocal operator containing a Wilson line; the choice in Wilson line path allows one to continuously interpolate from Ji to Jaffe-Manohar quark orbital angular momentum. The latter is seen to be significantly enhanced in magnitude compared to Ji quark orbital angular momentum, confirming previous results.
Generalized transverse momentum-dependent parton distributions (GTMDs) provide a comprehensive framework for imaging the internal structure of the proton. In particular, by encoding the simultaneous ...distribution of quark transverse positions and momenta, they allow one to directly access longitudinal quark orbital angular momentum, and, moreover, to correlate it with the quark helicity. The relevant GTMD is evaluated through a lattice calculation of a proton matrix element of a quark bilocal operator (the separation in which is Fourier conjugate to the quark momentum) featuring a momentum transfer (which is Fourier conjugate to the quark position), as well as the Dirac structure appropriate for capturing the quark helicity. The weighting by quark transverse position requires a derivative with respect to momentum transfer, which is obtained in unbiased fashion using a direct derivative method. The lattice calculation is performed directly at the physical pion mass, using domain wall fermions to mitigate operator mixing effects. Both the Jaffe-Manohar as well as the Ji quark spin-orbit correlations are extracted, yielding evidence for a strong quark spin-orbit coupling in the proton.
Quark orbital angular momentum (OAM) in the proton can be calculated directly given a Wigner function encoding the simultaneous distribution of quark transverse positions and momenta. This ...distribution can be accessed via proton matrix elements of a quark bilocal operator (the separation in which is Fourier conjugate to the quark momentum) featuring a momentum transfer (which is Fourier conjugate to the quark position). To generate the weighting by quark transverse position needed to calculate OAM, a derivative with respect to momentum transfer is consequently required. This derivative is evaluated using a direct derivative method, i.e., a method in which the momentum derivative of a correlator is directly sampled in the lattice calculation, as opposed to extracting it a posteriori from the numerical correlator data. The method removes the bias stemming from estimating the derivative a posteriori that was seen to afflict a previous exploratory calculation. Data for Ji OAM generated on a clover ensemble at pion mass \(m_{\pi } = 317\, \mbox{MeV} \) are seen to agree with the result obtained via the traditional Ji sum rule method. By varying the gauge connection in the quark bilocal operator, also Jaffe-Manohar OAM is extracted, and seen to be enhanced significantly compared to Ji OAM.
Co-thermolytical reactions of 1,1,2,2-tetrakis(dimethylamino)- or tetrakis(isopropylamino)dimethyldisilane
1 or
2 with 2,3-dimethylbuta-1,3-diene, 1,4-diheterodienes, 1-oxa- or 1-azadienes gave ...Si-functionalized unsaturated silicon heterocycles
3–
15. The disilanes act as precursors for intermediate aminosilylenes that undergo regioselective 1+4-cycloadditions with 2,3-dimethylbutadiene and 1,4-diheterodienes, affording silacyclopent-3-enes and diheterosilacyclopent-4-enes, respectively. Reactions with unsaturated ketones and imines gave isomer mixtures of 1-oxa- and 1-aza-2-silacyclopent-4-enes (major) and -3-enes (minor), indicating a stepwise mechanism. Co-thermolysis of
2 with 2,3-dimethylbutadiene, a diimine or iminoketone led to cycloaddition products of the NH functional Me(
iPrNH)Si, but yields were markedly lower than with
1.
FLAG Review 2021 Aoki, Y; Blum, T; Colangelo, G ...
arXiv.org,
10/2022
Paper, Journal Article
Odprti dostop
We review lattice results related to pion, kaon, \(D\)-meson, \(B\)-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More ...specifically, we report on the determination of the light-quark masses, the form factor \(f_+(0)\) arising in the semileptonic \(K \to \pi\) transition at zero momentum transfer, as well as the decay constant ratio \(f_K/f_\pi\) and its consequences for the CKM matrix elements \(V_{us}\) and \(V_{ud}\). Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of \(SU(2)_L\times SU(2)_R\) and \(SU(3)_L\times SU(3)_R\) Chiral Perturbation Theory. We review the determination of the \(B_K\) parameter of neutral kaon mixing as well as the additional four \(B\) parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for \(m_c\) and \(m_b\) as well as those for the decay constants, form factors, and mixing parameters of charmed and bottom mesons and baryons. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant \(\alpha_s\). We consider nucleon matrix elements, and review the determinations of the axial, scalar and tensor bilinears, both isovector and flavor diagonal. Finally, in this review we have added a new section reviewing determinations of scale-setting quantities.
Proceedings of Science (LATTICE2014) 372 In this write-up we review and update our recent lattice QCD calculation of
$B \to K^*$, $B_s \to \phi$, and $B_s \to K^*$ form factors arXiv:1310.3722.
These ...unquenched calculations, performed in the low-recoil kinematic regime,
provide a significant improvement over the use of extrapolated light cone sum
rule results. The fits presented here include further kinematic constraints and
estimates of additional correlations between the different form factor shape
parameters. We use these form factors along with Standard Model determinations
of Wilson coefficients to give Standard Model predictions for several
observables arXiv:1310.3887. The modest improvements to the form factor fits
lead to improved determinations of $F_L$, the fraction of longitudinally
polarized vector mesons, but have little effect on most other observables.
Two of the elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix, \(|V_{ub}|\) and \(|V_{cb}|\), are extracted from semileptonic B decays. The results of the B factories, analysed in the ...light of the most recent theoretical calculations, remain puzzling, because for both \(|V_{ub}|\) and \(|V_{cb}|\) the exclusive and inclusive determinations are in clear tension. Further, measurements in the \(\tau\) channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9--13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive B decays, and to exploit the rich possibilities at LHCb.
