5,973 research outputs found
Single grid accelerator for an ion thrustor
A single grid accelerator system for an ion thrustor is discussed. A layer of dielectric material is interposed between this metal grid and the chamber containing an ionized propellant for protecting the grid against sputtering erosion
Heegaard genus, cut number, weak p-congruence, and quantum invariants
We use quantum invariants to define a 3-manifold invariant j_p which lies in
the non-negative integers. We relate j_p to the Heegard genus, and the cut
number. We show that j_$ is an invariant of weak p-congruence.Comment: to appear in JKTR. 8pages 1 figur
Quantum -core conduction on the Bethe lattice
Classical and quantum conduction on a bond-diluted Bethe lattice is
considered. The bond dilution is subject to the constraint that every occupied
bond must have at least neighboring occupied bonds, i.e. -core
diluted. In the classical case, we find the onset of conduction for is
continuous, while for , the onset of conduction is discontinuous with the
geometric random first-order phase transition driving the conduction
transition. In the quantum case, treating each occupied bond as a random
scatterer, we find for that the random first-order phase transition in
the geometry also drives the onset of quantum conduction giving rise to a new
universality class of Anderson localization transitions.Comment: 12 pgs., 6 fig
Non-ideal behavior of intramolecular structure factor of dilute polymers in a theta solvent
We study the configurational properties of single polymers in a theta solvent
by Monte Carlo simulation of the bond fluctuation model. The intramolecular
structure factor at the theta point is found to be distinctively different from
that of the ideal chain. The structure factor shows a hump around
and a dip around in the Kratky plot with being the radius
of gyration. This feature is apparently similar to that in a melt. The
theoretical expression by the simple perturbation expansion to the first order
in terms of the Mayer function can be fitted to the obtained structure factor
quite well, but the second virial coefficient cannot be set to zero.Comment: 8 pages, 7figure
Millimeter Interferometric Investigations of the Energy Sources of Three Ultraluminous Infrared Galaxies, UGC 5101, Mrk 273, and IRAS 17208-0014, based on HCN to HCO+ Ratios
We present interferometric observations of three ultraluminous infrared
galaxies (ULIRGs; UGC 5101, Mrk 273, and IRAS 17208-0014) in the 3-mm
wavelength range, using the Nobeyama Millimeter Array. Both the HCN (J=1-0) and
HCO+ (J=1-0) molecular lines were observed simultaneously. HCN emission was
clearly detected at the nuclear positions of these ULIRGs, and HCO+ emission
was detected at the nuclear positions of UGC 5101 and IRAS 17208-0014. The HCN
to HCO+ brightness-temperature ratios toward the nuclei of the three ULIRGs
were derived and compared with those of lower luminosity galaxies known to be
dominated by active galactic nuclei (AGNs) or starbursts. In UGC 5101 and Mrk
273, where there is evidence for obscured AGNs from previous observations at
other wavelengths, we found high HCN/HCO+ ratios (>1.8) that are in the range
found for AGN-dominated galaxies. In IRAS 17208-0014, where the presence of a
powerful obscured AGN has been unclear, the ratio (1.7) is in between the
observed values for starburst- and AGN-dominated galaxies. The high HCN/HCO+
brightness-temperature ratios in UGC 5101 and Mrk 273 could be the consequence
of an HCN abundance enhancement, which is expected from chemical effects of the
central X-ray emitting AGN on the surrounding dense molecular gas. Our proposed
millimeter interferometric method based on HCN/HCO+ ratios may be an effective
tool for unveiling elusive buried AGNs at the cores of ULIRGs, especially
because of the negligible dust extinction at these wavelengths.Comment: 15 pages (emulateapj.sty), 8 figures (figures 1-5 resolution
reduced), Accepted for publication in Astronomical Journal, A PDF file with
high resolution is availble at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN/HCN.pd
Markov chain analysis of random walks on disordered medium
We study the dynamical exponents and for a particle diffusing
in a disordered medium (modeled by a percolation cluster), from the regime of
extreme disorder (i.e., when the percolation cluster is a fractal at )
to the Lorentz gas regime when the cluster has weak disorder at and
the leading behavior is standard diffusion. A new technique of relating the
velocity autocorrelation function and the return to the starting point
probability to the asymptotic spectral properties of the hopping transition
probability matrix of the diffusing particle is used, and the latter is
numerically analyzed using the Arnoldi-Saad algorithm. We also present evidence
for a new scaling relation for the second largest eigenvalue in terms of the
size of the cluster, , which provides a
very efficient and accurate method of extracting the spectral dimension
where .Comment: 34 pages, REVTEX 3.
An Interaction of a Magellanic Leading Arm High Velocity Cloud with the Milky Way Disk
The Leading Arm of the Magellanic System is a tidally formed HI feature
extending \sim 60\arcdeg from the Magellanic Clouds ahead of their direction
of motion. Using atomic hydrogen (HI) data from the Galactic All Sky-Survey
(GASS), supplemented with data from the Australia Telescope Compact Array, we
have found evidence for an interaction between a cloud in the Leading Arm and
the Galactic disk where the Leading Arm crosses the Galactic plane. The
interaction occurs at velocities permitted by Galactic rotation, which allows
us to derive a kinematic distance to the cloud of 21 kpc, suggesting that the
Leading Arm crosses the Galactic Plane at a Galactic radius of
kpc.Comment: 14 pages, 5 figures, accepted to Astrophysical Journal Letters. Full
resolution version available at
ftp://ftp.atnf.csiro.au/pub/people/nmcclure/papers/LeadingArm_apjl.pd
Absorption-free optical control of spin systems:the quantum Zeno effect in optical pumping
We show that atomic spin motion can be controlled by circularly polarized
light without light absorption in the strong pumping limit. In this limit, the
pumping light, which drives the empty spin state, destroys the Zeeman coherence
effectively and freezes the coherent transition via the quantum Zeno effect. It
is verified experimentally that the amount of light absorption decreases
asymptotically to zero as the incident light intensity is increased.Comment: 4 pages with 4 figure
A New Symmetry for QED
We demonstrate that QED exhibits a previously unobserved symmetry. Some
consequences are discussed.Comment: 9 pages, MZ-TH/93-02, DIAS-STP-93-0
Hadronic unquenching effects in the quark propagator
We investigate hadronic unquenching effects in light quarks and mesons.
Within the non-perturbative continuum framework of Schwinger-Dyson and
Bethe-Salpeter equations we quantify the strength of the back reaction of the
pion onto the quark-gluon interaction. To this end we add a Yang-Mills part of
the interaction such that unquenched lattice results for various current quark
masses are reproduced. We find considerable effects in the quark mass function
at low momenta as well as for the chiral condensate. The quark wave function is
less affected. The Gell--Mann-Oakes-Renner relation is valid to good accuracy
up to pion masses of 400-500 MeV. As a byproduct of our investigation we verify
the Coleman theorem, that chiral symmetry cannot be broken spontaneously when
QCD is reduced to 1+1 dimensions.Comment: 27 pages, 15 figures, minor corrections and clarifications; version
to appear in PR
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