97 research outputs found

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    The Antiferroelectric ↔ Ferroelectric Phase Transition in Lead-Containing and Lead-Free Perovskite Ceramics

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    A comprehensive review on the latest development of the antiferroelectric ferroelectric phase transition is presented. The abrupt volume expansion and sudden development of polarization at the phase transition has been extensively investigated in PbZrO3-based perovskite ceramics. New research developments in these compositions, including the incommensurate domain structure, the auxetic behavior under electric fields in the induced ferroelectric phase, the ferroelastic behavior of the multicell cubic phase, the impact of radial compression, the unexpected electric field-induced ferroelectric-to-antiferroelectric transition, and the phase transition mechanical toughening effect have been summarized. Due to their significance to lead-free piezoelectric ceramics, compounds with antiferroelectric phases, including NaNbO3, AgNbO3, and (Bi1/2Na1/2)TiO3, are also critically reviewed. Focus has been placed on the (Bi1/2Na1/2)TiO3–BaTiO3 solid solution where the electric field-induced ferroelectric phase remains even after the applied field is removed at room temperature. Therefore, the electric field-induced antiferroelectric-to-ferroelectric phase transition is a key to the poling process to develop piezoelectricity in morphotropic phase boundary (MPB) compositions. The competing phase transition and domain switching processes in 0.93(Bi1/2Na1/2)TiO3–0.07BaTiO3 are directly imaged with nanometer resolution using the unique in situ transmission electron microscopy (TEM) technique

    ϕ\phi meson production in dd++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

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    The PHENIX experiment has measured ϕ\phi meson production in dd++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV using the dimuon and dielectron decay channels. The ϕ\phi meson is measured in the forward (backward) dd-going (Au-going) direction, 1.2<y<2.21.2<y<2.2 (2.2<y<1.2-2.2<y<-1.2) in the transverse-momentum (pTp_T) range from 1--7 GeV/cc, and at midrapidity y<0.35|y|<0.35 in the pTp_T range below 7 GeV/cc. The ϕ\phi meson invariant yields and nuclear-modification factors as a function of pTp_T, rapidity, and centrality are reported. An enhancement of ϕ\phi meson production is observed in the Au-going direction, while suppression is seen in the dd-going direction, and no modification is observed at midrapidity relative to the yield in pp++pp collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor indicating similar cold-nuclear-matter effects.Comment: 484 authors, 16 pages, 12 figures, 6 tables. v1 is the version accepted for publication in Phys. Rev. C. Data tables for the points plotted in the figures are given in the paper itsel

    Single electron yields from semileptonic charm and bottom hadron decays in Au++Au collisions at sNN=200\sqrt{s_{NN}}=200 GeV

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    The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy-flavor production in minimum bias Au++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons. Previous heavy-flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks due to the quark-gluon plasma created in these collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking, the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum are measured in Au++Au collisions. We compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in pp++pp collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV and find the fractions to be similar within the large uncertainties on both measurements for pT>4p_T>4 GeV/cc. We use the bottom electron fractions in Au++Au and pp++pp along with the previously measured heavy flavor electron RAAR_{AA} to calculate the RAAR_{AA} for electrons from charm and bottom hadron decays separately. We find that electrons from bottom hadron decays are less suppressed than those from charm for the region 3<pT<43<p_T<4 GeV/cc.Comment: 432 authors, 33 pages, 23 figures, 2 tables, 2011 data. v2 is version accepted for publication by Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

    Cross Section and Transverse Single-Spin Asymmetry of η\eta Mesons in p+pp^{\uparrow}+p Collisions at s=200\sqrt{s}=200 GeV at Forward Rapidity

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    We present a measurement of the cross section and transverse single-spin asymmetry (ANA_N) for η\eta mesons at large pseudorapidity from s=200\sqrt{s}=200~GeV p+pp^{\uparrow}+p collisions. The measured cross section for 0.5<pT<5.00.5<p_T<5.0~GeV/cc and 3.0<η<3.83.0<|\eta|<3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries ANA_N have been measured as a function of Feynman-xx (xFx_F) from 0.2<xF<0.70.2<|x_{F}|<0.7, as well as transverse momentum (pTp_T) from 1.0<pT<4.51.0<p_T<4.5~GeV/cc. The asymmetry averaged over positive xFx_F is AN=0.061±0.014\langle{A_{N}}\rangle=0.061{\pm}0.014. The results are consistent with prior transverse single-spin measurements of forward η\eta and π0\pi^{0} mesons at various energies in overlapping xFx_F ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p+pp^{\uparrow}+p collisions.Comment: 484 authors, 13 pages, 11 figures, 4 tables, 2008 data. v2 is version accepted by Phys. Rev. D. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be)publicly available at http://www.phenix.bnl.gov/papers.htm

    Systematic study of charged-pion and kaon femtoscopy in Au++Au collisions at sNN\sqrt{s_{_{NN}}}=200 GeV

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    We present a systematic study of charged pion and kaon interferometry in Au++Au collisions at sNN\sqrt{s_{_{NN}}}=200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.Comment: 499 authors, 27 pages, 13 figures, and 11 tables. v2 is the version accepted for publication in Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm
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