1,251,331 research outputs found
Density-functional theory of polar insulators
We examine the density-functional theory of macroscopic insulators, obtained in the large-cluster limit or under periodic boundary conditions. For polar crystals, we find that the two procedures are not equivalent. In a large-cluster case, the exact exchange-correlation potential acquires a homogeneous ``electric field'' which is absent from the usual local approximations, and the Kohn-Sham electronic system becomes metallic. With periodic boundary conditions, such a field is forbidden, and the polarization deduced from Kohn-Sham wavefunctions is incorrect even if the exact functional is used
Reinforced metallic composites Patent
High strength reinforced metallic composites for applications over wide temperature rang
Fragment isospin distributions and the phase diagram of excited nuclear systems
Fragment average isospin distributions are investigated within a
microcanonical multifragmentation model in different regions of the phase
diagram. The results indicate that in the liquid phase versus is
monotonically increasing, in the phase coexistence region it has a rise and
fall shape and in the gas phase it is constant. Deviations from this behavior
may manifest at low fragment multiplicity as a consequence of mass/charge
conservation. Characterization of the "free" and "bound" phases function of
fragment charge reconfirms the neutron enrichment of the "free" phase with
respect to the "bound" one irrespectively the localization of the
multifragmentation event in the phase diagram.Comment: 23 pages, 12 figure
Herschel-PACS observation of the 10 Myr old T Tauri disk TW Hya: Constraining the disk gas mass
Planets are formed in disks around young stars. With an age of ~10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TWHya disk, making TWHya the perfect test case in a large
survey of disks with Herschel–PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [O_I] and [C_(II)] as part of the open-time large program GASPS. We complement this
with continuum data and ground-based ^(12)CO 3–2 and ^(13)CO 3–2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [O_I] line at 63 μm. The other lines that were observed, [O_I] at 145 μm and [C_(II)] at 157 μm, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [^(12)CO]/[^(13)CO] = 69 suggests a dust mass for grains with radius <1 mm of ~1.9 × 10^(−4) M_⊙ (total solid mass of 3 × 10^(−3) M_⊙) and a gas mass of (0.5–5) ×10^(−3) M_⊙. The gas-to-dust mass may be lower than the standard interstellar value of 100
Extracting nucleon strange and anapole form factors from world data
The complete world set of parity violating electron scattering data up to
Q^2~0.3 GeV^2 is analysed. We extract the current experimental determination of
the strange electric and magnetic form factors of the proton, as well as the
weak axial form factors of the proton and neutron, at Q^2 = 0.1 GeV^2. Within
experimental uncertainties, we find that the strange form factors are
consistent with zero, as are the anapole contributions to the axial form
factors. Nevertheless, the correlation between the strange and anapole
contributions suggest that there is only a small probability that these form
factors all vanish simultaneously.Comment: 4 pages, 3 figs; v2: version to appear in PR
Chiral and Continuum Extrapolation of Partially-Quenched Lattice Results
The vector meson mass is extracted from a large sample of partially quenched,
two-flavor lattice QCD simulations. For the first time, discretisation,
finite-volume and partial quenching artefacts are treated in a unified
framework which is consistent with the low-energy behaviour of QCD. This
analysis incorporates the leading infrared behaviour dictated by chiral
effective field theory. As the two-pion decay channel cannot be described by a
low-energy expansion alone, a highly-constrained model for the decay channel of
the rho-meson is introduced. The latter is essential for extrapolating lattice
results from the quark-mass regime where the rho is observed to be a physical
bound state.Comment: 9 pages, 3 figures; revised version appearing in PL
Chiral and Continuum Extrapolation of Partially-Quenched Hadron Masses
Using the finite-range regularisation (FRR) of chiral effective field theory,
the chiral extrapolation formula for the vector meson mass is derived for the
case of partially-quenched QCD. We re-analyse the dynamical fermion QCD data
for the vector meson mass from the CP-PACS collaboration. A global fit,
including finite lattice spacing effects, of all 16 of their ensembles is
performed. We study the FRR method together with a naive polynomial approach
and find excellent agreement ~1% with the experimental value of M_rho from the
former approach. These results are extended to the case of the nucleon mass.Comment: 6 pages, Contribution to Lattice2005, PoS styl
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