130,411 research outputs found
Development of a Straw Tube Chamber with Pickup-Pad Readout
We have developed a straw tube chamber with pickup-pad readout. The mechanism
for signal pickup, the size of the pickup signal, and the distribution of
signals among neighboring pads are discussed. We have tested a prototype
chamber in a beamtest at Brookhaven National laboratory and have measured
chamber efficiencies in excess of 99%.Comment: 7 pages, 8 figures, 2 tables. Talk presented at DPF '99 Meeting, UCL
Variability in Proto-Planetary Nebulae: IV. Light Curve Analyses of Four Oxygen-Rich, F Spectral-Type Objects
We present new light curves covering 14 to 19 years of observations of four
bright proto-planetary nebulae (PPNs), all O-rich and of F spectral type. They
each display cyclical light curves with significant variations in amplitude.
All four were previously known to vary in light. Our data were combined with
published data and searched for periodicity. The results are as follows: IRAS
19475+3119 (HD 331319; 41.0 days), 17436+5003 (HD 161796; 45.2 days),
19386+0155 (101.8 days), and 18095+2704 (113.3 days). The two longer periods
are in agreement with previous studies while the two shorter periods each
reveal for the first time reveal a dominant period over these long observing
intervals. Multiple periods were also found for each object. The secondary
periods were all close to the dominant periods, with P2/P1 ranging from 0.86 to
1.06. The variations in color reveal maximum variations in T(eff) of 400 to 770
K. These variations are due to pulsations in these post-AGB objects. Maximum
seasonal light variations are all less than 0.23 mag (V), consistent for their
temperatures and periods with the results of Hrivnak et al. (2010) for 12
C-rich PPNs. For all of these PPNs, there is an inverse relationship between
period and temperature; however, there is a suggestion that the
period-temperature relationship may be somewhat steeper for the O-rich than for
the C-rich PPNs.Comment: 28 pages, 13 figures, to appear in the Astronomical Journa
Triaxiality and shape coexistence in Germanium isotopes
The ground-state deformations of the Ge isotopes are investigated in the
framework of Gogny-Hartree-Fock-Bogoliubov (HFB) and Skyrme Hartree-Fock plus
pairing in the BCS approximation. Five different Skyrme parametrizations are
used to explore the influence of different effective masses and spin-orbit
models. There is generally good agreement for binding energies and deformations
(total quadrupole moment, triaxiality) with experimental data where available
(i.e., in the valley of stability). All calculations agree in predicting a
strong tendency for triaxial shapes in the Ge isotopes with only a few
exceptions due to neutron (sub-)shell closures. The frequent occurrence of
energetically very close shape isomers indicates that the underlying
deformation energy landscape is very soft. The general triaxial softness of the
Ge isotopes is demonstrated in the fully triaxial potential energy surface. The
differences between the forces play an increasing role with increasing neutron
number. This concerns particularly the influence of the spin-orbit model, which
has a visible effect on the trend of binding energies towards the drip line.
Different effective mass plays an important role in predicting the quadrupole
and triaxial deformations. The pairing strength only weakly affects binding
energies and total quadrupole deformations, but considerably influences
triaxiality.Comment: 9 page
The black hole mass versus velocity dispersion relation in QSOs/Active Galactic Nuclei: observational appearance and black hole growth
Studies of massive black holes (BHs) in nearby galactic centers have revealed
a tight correlation between BH mass and galactic velocity dispersion. In this
paper we investigate how the BH mass versus velocity dispersion relation and
the nuclear luminosity versus velocity dispersion relation in QSOs/active
galactic nuclei (AGNs) are connected with the BH mass versus velocity
dispersion relation in local galaxies, through the nuclear luminosity evolution
of individual QSOs/AGNs and the mass growth of individual BHs. In the study we
ignore the effects of BH mergers and assume that the velocity dispersion does
not change significantly during and after the nuclear activity phase. Using the
observed correlation in local galaxies and an assumed form of the QSO/AGN
luminosity evolution and BH growth, we obtain the simulated observational
appearance of the BH mass versus velocity dispersion relation in QSOs/AGNs. The
simulation results illustrate how the BH accretion history (e.g., the lifetime
of nuclear activity and the possibility that QSOs/AGNs accrete at a
super-Eddington accretion rate at the early evolutionary stage) can be inferred
from the difference between the relation in QSOs/AGNs and that in local
galaxies. We also show how the difference may be weakened by the flux limit of
telescopes. We expect that a large complete sample of QSOs/AGNs with accurate
BH mass and velocity dispersion measurements will help to quantitatively
constrain QSO/AGN luminosity evolution and BH growth models.Comment: 20 pages, including 4 figures; revised to match the published versio
Gaussian Effective Potential and the Coleman's normal-ordering Prescription : the Functional Integral Formalism
For a class of system, the potential of whose Bosonic Hamiltonian has a
Fourier representation in the sense of tempered distributions, we calculate the
Gaussian effective potential within the framework of functional integral
formalism. We show that the Coleman's normal-ordering prescription can be
formally generalized to the functional integral formalism.Comment: 6 pages, revtex; With derivation details and an example added. To
appear in J. Phys.
The Generalized Crewther Relation in QCD and its Experimental Consequences
We use the BLM scale-fixing prescription to derive a renormalization-scheme
invariant relation between the coefficient function for the Bjorken sum rule
for polarized deep inelastic scattering and the -ratio for the
annihilation cross section. This relation provides a generalization of the
Crewther relation to non-conformally invariant gauge theories. The derived
relations allow one to calculate unambiguously without renormalization scale or
scheme ambiguity the effective charges of the polarized Bjorken and the
Gross-Llewellen Smith sum rules from the experimental value for the effective
charge associated with -ratio. Present data are consistent with the
generalized Crewther relations, but measurements at higher precision and
energies will be needed to decisively test these fundamental relations in QCD.Comment: 16 pages, LATEX fil
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