36,467 research outputs found

### Skyrme-force time-dependent Hartree-Fock calculations with axial symmetry

We discuss axially symmetric time-dependent Hartree-Fock calculations using a finite-range modification of the Skyrme energy functional. The finite-difference forms of the coordinate-space time-dependent Hartree-Fock equations, the method of time evolution, and other numerical aspects are presented. Detailed results for (^84)Kr-induced deep-inelastic collisions with (^208)Pb at E_(lab) = 494 MeV and with (^209)Bi at E_(lab) = 600 MeV and 714 MeV are compared with experiment.
[NUCLEAR REACTIONS (^84)Kr + (^208)Pb at E_lab = 494 MeV and (^84)Kr + (^209)Bi at E_1ab=600 and 714 MeV, in the time-dependent Hartree-Fock approximation. Strongy
damped collisions. Details of Skyrme force calculations with axial symmetry.

### Progress in materials and structures at Lewis Research Center

The development of power and propulsion system technology is discussed. Specific emphasis is placed on the following: high temperature materials; composite materials; advanced design and life prediction; and nondestructive evaluation. Future areas of research are also discussed

### Smearing effect due to the spread of a probe-particle on the Brownian motion near a perfectly reflecting boundary

Quantum fluctuations of electromagnetic vacuum are investigated in a
half-space bounded by a perfectly reflecting plate by introducing a probe
described by a charged wave-packet distribution in time-direction. The
wave-packet distribution of the probe enables one to investigate the smearing
effect upon the measured vacuum fluctuations caused by the quantum nature of
the probe particle. It is shown that the wave-packet spread of the probe
particle significantly influences the measured velocity dispersion of the
probe. In particular, the asymptotic late-time behavior of its $z$-component, , for the wave-packet case is quite different from the test
point-particle case ($z$ is the coordinate normal to the plate). The result for
the wave-packet is \sim 1/\t^2 in the late time (\t is the
measuring time), in stead of the reported late-time behavior $\sim 1/z^2$ for a point-particle probe. This result can be quite significant
for further investigations on the measurement of vacuum fluctuations.Comment: 8 page

### A strong 3.4 micron emission feature in comet Austin 1989c1

High resolution 2.8-4.0 micron spectra of the 'new' comet Austin 1989c1, taken on 15-16 May 1990 confirm the presence of the broad emission features around 3.4 and 3.52 micron seen in a number of bright comets and ascribed to organic material. Both the 3.4 micron band strength and the 3.52/3.36 micron flux ratios are among the largest so far observed. The data are consistent with the relationship between band strength and water production rate that was recently derived. Excess emission at 3.28 and 3.6 micron cannot be unambiguously identified as features due to the poor signal-to-noise ratio

### The Tenerife Cosmic Microwave Background Maps: Observations and First Analysis

The results of the Tenerife Cosmic Microwave Background (CMB) experiments are
presented. These observations cover 5000 and 6500 square degrees on the sky at
10 and 15 GHz respectively centred around Dec.~ +35 degrees. The experiments
are sensitive to multipoles l=10-30 which corresponds to the Sachs-Wolfe
plateau of the CMB power spectra. The sensitivity of the results are ~31 and
\~12 microK at 10 and 15 GHz respectively in a beam-size region (5 degrees
FWHM). The data at 15 GHz show clear detection of structure at high Galactic
latitude; the results at 10 GHz are compatible with these, but at lower
significance. A likelihood analysis of the 10 and 15 GHz data at high Galactic
latitude, assuming a flat CMB band power spectra gives a signal Delta
T_l=30+10-8 microK (68 % C.L.). Including the possible contaminating effect due
to the diffuse Galactic component, the CMB signal is Delta T_l=30+15-11 microK.
These values are highly stable against the Galactic cut chosen. Assuming a
Harrison-Zeldovich spectrum for the primordial fluctuations, the above values
imply an expected quadrupole Q_RMS-PS=20+10-7 microK which confirms previous
results from these experiments, and which are compatible with the COBE DMR.Comment: 17 pages, 7 figures. Submitted to Ap

### Microscopic sub-barrier fusion calculations for the neutron star crust

Fusion of very neutron rich nuclei may be important to determine the
composition and heating of the crust of accreting neutron stars. Fusion cross
sections are calculated using time-dependent Hartree-Fock theory coupled with
density-constrained Hartree-Fock calculations to deduce an effective potential.
Systems studied include 16O+16O, 16O+24O, 24O+24O, 12C+16O, and 12C+24O. We
find remarkable agreement with experimental cross sections for the fusion of
stable nuclei. Our simulations use the SLy4 Skyrme force that has been
previously fit to the properties of stable nuclei, and no parameters have been
fit to fusion data. We compare our results to the simple S\~{a}o Paulo static
barrier penetration model. For the asymmetric systems 12C+24O or 16O+24O we
predict an order of magnitude larger cross section than those predicted by the
S\~{a}o Paulo model. This is likely due to the transfer of neutrons from the
very neutron rich nucleus to the stable nucleus and dynamical rearrangements of
the nuclear densities during the collision process. These effects are not
included in potential models. This enhancement of fusion cross sections, for
very neutron rich nuclei, can be tested in the laboratory with radioactive
beams.Comment: 9 pages, 11 figures, corrected small errors in Figs 10, 11, Phys.
Rev. C in pres

### Predicting morphotropic phase boundary locations and transition temperatures in Pb- and Bi-based perovskite solid solutions from crystal chemical data and first-principles calculations

Using data obtained from first-principles calculations, we show that the
position of the morphotropic phase boundary (MPB) and transition temperature at
MPB in ferroelectric perovskite solutions can be predicted with quantitative
accuracy from the properties of the constituent cations. We find that the mole
fraction of PbTiO$_3$ at MPB in Pb(B$'$B$''$)O$_3$-PbTiO$_3$,
BiBO$_3$-PbTiO$_3$ and Bi(B$'$B$''$)O$_3$-PbTiO$_3$ exhibits a linear
dependence on the ionic size (tolerance factor) and the ionic displacements of
the B-cations as found by density functional theory calculations. This
dependence is due to competition between the local repulsion and A-cation
displacement alignment interactions. Inclusion of first-principles displacement
data also allows accurate prediction of transiton temperatures at the MPB. The
obtained structure-property correlations are used to predict morphotropic phase
boundaries and transition temperatures in as yet unsynthesized solid solutions.Comment: Accepted for publication in J. Appl. Phy

### Spin-Excitation Mechanisms in Skyrme-Force Time-Dependent Hartree-Fock

We investigate the role of odd-odd (with respect to time inversion) couplings
in the Skyrme force on collisions of light nuclei, employing a fully
three-dimensional numerical treatment without any symmetry restrictions and
with modern Skyrme functionals. We demonstrate the necessity of these couplings
to suppress spurious spin excitations owing to the spin-orbit force in free
translational motion of a nucleus but show that in a collision situation there
is a strong spin excitation even in spin-saturated systems which persists in
the departing fragments. The energy loss is considerably increased by the
odd-odd terms

### Υ and Υ′ leptonic widths, abμ, and mb from full lattice QCD

We determine the decay rate to leptons of the ground-state ϒ meson and its first radial excitation in lattice
QCD for the first time. We use radiatively improved nonrelativistic QCD for the b quarks and include u, d,
s and c quarks in the sea with u=d masses down to their physical values. We find Γðϒ → eþe−Þ ¼
1.19ð11Þ keV and Γðϒ0 → eþe−Þ ¼ 0.69ð9Þ keV, both in good agreement with experimental results. The
decay constants we obtain are included in a summary plot of meson decay constants from lattice QCD
given in the Conclusions. We also test time moments of the vector current-current correlator against values
determined from the b-quark contribution to σðeþe− → hadronsÞ and calculate the b-quark piece of the
hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon,
ab
μ ¼ 0.271ð37Þ × 10−10. Finally we determine the b-quark mass, obtaining in the MS scheme, ¯
m¯ bðm¯ b; nf ¼ 5Þ ¼ 4.196ð23Þ GeV, the most accurate result from lattice QCD to date

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