814 research outputs found
The lunar surface as a recorder of astrophysical processes
The lunar surface has been exposed to the space environment for billions of years and during this time has
accumulated records of a wide range of astrophysical phenomena. These include solar wind particles and the
cosmogenic products of solar particle events which preserve a record of the past evolution of the Sun, and
cosmogenic nuclides produced by high-energy galactic cosmic rays which potentially record the galactic
environment of the Solar System through time. The lunar surface may also have accreted material from the local
interstellar medium, including supernova ejecta and material from interstellar clouds encountered by the Solar
System in the past. Owing to the Moon’s relatively low level of geological activity, absence of an atmosphere,
and, for much of its history, lack of a magnetic field, the lunar surface is ideally suited to collect these
astronomical records. Moreover, the Moon exhibits geological processes able to bury and thus both preserve
and ‘time-stamp’ these records, although gaining access to them is likely to require a significant scientific
infrastructure on the lunar surface
Str\"omgren photometry and spectroscopy of the Delta Scuti stars 7 Aql and 8 Aql
Photometric ) and spectroscopic observations of the
Scuti variables \astrobj{7 Aql} and \astrobj{8 Aql} are described. The
Str\"omgren standard indices and physical parameters of both stars are derived.
Spectral types of F0V and F2III have been assigned to \astrobj{7 Aql} and
\astrobj{8 Aql} respectively considering the results from both spectroscopy and
photometry. Differential light curves were also analyzed. A attempt of
multicolour mode identification is carried out.Comment: 6 pages, 7 figures, 4 tables, accepted for publication in New
Astronom
Systematic Cu-63 NQR studies of the stripe phase in La(1.6-x)Nd(0.4)Sr(x)CuO(4) for 0.07 <= x <= 0.25
We demonstrate that the integrated intensity of Cu-63 nuclear quadrupole
resonance (NQR) in La(1.6-x)Nd(0.4)Sr(x)CuO(4) decreases dramatically below the
charge-stripe ordering temperature T(charge). Comparison with neutron and X-ray
scattering indicates that the wipeout fraction F(T) (i.e. the missing fraction
of the integrated intensity of the NQR signal) represents the charge-stripe
order parameter. The systematic study reveals bulk charge-stripe order
throughout the superconducting region 0.07 <= x <= 0.25. As a function of the
reduced temperature t = T/T(charge), the temperature dependence of F(t) is
sharpest for the hole concentration x=1/8, indicating that x=1/8 is the optimum
concentration for stripe formation.Comment: 10 pages of text and captions, 11 figures in postscript. Final
version, with new data in Fig.
Berry phases and pairing symmetry in Holstein-Hubbard polaron systems
We study the tunneling dynamics of dopant-induced hole polarons which are
self-localized by electron-phonon coupling in a two-dimensional antiferro-
magnet. Our treatment is based on a path integral formulation of the adia-
batic approximation, combined with many-body tight-binding, instanton, con-
strained lattice dynamics, and many-body exact diagonalization techniques. Our
results are mainly based on the Holstein- and, for comparison, on the
Holstein-Hubbard model. We also study effects of 2nd neighbor hopping and
long-range electron-electron Coulomb repulsion. The polaron tunneling dynamics
is mapped onto an effective low-energy Hamiltonian which takes the form of a
fermion tight-binding model with occupancy dependent, predominant- ly 2nd and
3rd neighbor tunneling matrix elements, excluded double occupan- cy, and an
effective intersite charge interactions. Antiferromagnetic spin correlations in
the original many-electron Hamiltonian are reflected by an attractive
contribution to the 1st neighbor charge interaction and by Berry phase factors
which determine the signs of effective polaron tunneling ma- trix elements. In
the two-polaron case, these phase factors lead to polaron pair wave functions
of either -wave symmetry or p-wave symme- try with zero and
nonzero total pair momentum, respectively. Implications for the doping
dependent isotope effect, pseudo-gap and Tc of a superconduc- ting polaron pair
condensate are discussed/compared to observed in cuprates.Comment: 23 pages, revtex, 13 ps figure
Interplay of Electron-Phonon Interaction and Electron Correlation in High Temperature Superconductivity
We study the electron-phonon interaction in the strongly correlated
superconducting cuprates. Two types of the electron-phonon interactions are
introduced in the model; the diagonal and off-diagonal interactions which
modify the formation energy of the Zhang-Rice singlet and its transfer
integral, respectively. The characteristic phonon-momentum and
electron-momentum dependence resulted from the off-diagonal coupling
can explain a variety of experiments. The vertex correction for the
electron-phonon interaction is formulated in the SU(2) slave-boson theory by
taking into account the collective modes in the superconducting ground states.
It is shown that the vertex correction enhances the attractive potential for
the d-wave paring mediated by phonon with around
which corresponds to the half-breathing mode of the oxygen
motion.Comment: 14 pages, 13 figure
Au+Au Reactions at the AGS: Experiments E866 and E917
Particle production and correlation functions from Au+Au reactions have been
measured as a function of both beam energy (2-10.7AGeV) and impact parameter.
These results are used to probe the dynamics of heavy-ion reactions, confront
hadronic models over a wide range of conditions and to search for the onset of
new phenomena.Comment: 12 pages, 14 figures, Talk presented at Quark Matter '9
Single Spin Asymmetry in Polarized Proton-Proton Elastic Scattering at GeV
We report a high precision measurement of the transverse single spin
asymmetry at the center of mass energy GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The was measured
in the four-momentum transfer squared range \GeVcSq, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
and its -dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this , we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
High non-photonic electron production in + collisions at = 200 GeV
We present the measurement of non-photonic electron production at high
transverse momentum ( 2.5 GeV/) in + collisions at
= 200 GeV using data recorded during 2005 and 2008 by the STAR
experiment at the Relativistic Heavy Ion Collider (RHIC). The measured
cross-sections from the two runs are consistent with each other despite a large
difference in photonic background levels due to different detector
configurations. We compare the measured non-photonic electron cross-sections
with previously published RHIC data and pQCD calculations. Using the relative
contributions of B and D mesons to non-photonic electrons, we determine the
integrated cross sections of electrons () at 3 GeV/10 GeV/ from bottom and charm meson decays to be = 4.0({\rm
stat.})({\rm syst.}) nb and =
6.2({\rm stat.})({\rm syst.}) nb, respectively.Comment: 17 pages, 17 figure
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