5,682 research outputs found
On Observing Dynamic Prioritised Actions in SOC
We study the impact on observational semantics for SOC of priority mechanisms which combine dynamic priority with local pre-emption. We define manageable notions of strong and weak labelled bisimilarities for COWS, a process calculus for SOC, and provide alternative characterisations in terms of open barbed bisimilarities. These semantics show that COWSâs priority mechanisms partially recover the capability to observe receive actions (that could not be observed in a purely asynchronous setting) and that high priority primitives for termination impose specific conditions on the bisimilarities
Persistent superfluid phase in a three-dimensional quantum XY model with ring exchange
We present quantum Monte Carlo simulation results on a quantum S=1/2 XY model
with ring exchange (the J-K model) on a three-dimensional simple cubic lattice.
We first characterize the ground state properties of the pure XY model,
obtaining estimations for the energy, spin stiffness and spin susceptibility at
T=0 in the superfluid phase. With the ring exchange, we then present simulation
data on small lattices which suggests that the superfluid phase persists to
very large values of the ring exchange K, without signatures of a phase
transition. We comment on the consequences of this result for the search for
various exotic phases in three dimensions.Comment: 4 pages, 4 figure
Field-induced 3- and 2-dimensional freezing in a quantum spin liquid
Field-induced commensurate transverse magnetic ordering is observed in the
Haldane-gap compound \nd by means of neutron diffraction. Depending on the
direction of applied field, the high-field phase is shown to be either a
3-dimensional ordered N\'{e}el state or a short-range ordered state with
dominant 2-dimensional spin correlations. The structure of the high-field phase
is determined, and properties of the observed quantum phase transition are
discussed.Comment: 4 pages 3 figure
Covariation Among Vowel Height Effects on Acoustic Measures
Covariation among vowel height effects on vowel intrinsic fundamental frequency (IF0), voice onset time (VOT), and voiceless interval duration (VID) is analyzed to assess the plausibility of a common physiological mechanism underlying variation in these measures. Phrases spoken by 20 young adults, containing words composed of initial voiceless stops or /s/ and high or low vowels, were produced in habitual and voluntarily increased F0 conditions. High vowels were associated with increased IF0 and longer VIDs. VOT and VID exhibited significant covariation with IF0 only for males at habitua
Field-Induced Transition in the S=1 Antiferromagnetic Chain with Single-Ion Anisotropy in a Transverse Magnetic Field
The field-induced transition in one-dimensional S=1 Heisenberg
antiferromagnet with single-ion anisotropy in the presence of a transverse
magnetic field is obtained on the basis of the Schwinger boson mean-field
theory. The behaviors of the specific heat and susceptibility as functions of
temperature as well as the applied transverse field are explored, which are
found to be different from the results obtained under a longitudinal field. The
anomalies of the specific heat at low temperatures, which might be an
indicative of a field-induced transition from a Luttinger liquid phase to an
ordered phase, are explicitly uncovered under the transverse field. A schematic
phase diagram is proposed. The theoretical results are compared with
experimental observations.Comment: Revtex, 7 figure
Electronic transport properties of quasicrystals: a Review
We present a review of some results concerning electronic transport
properties of quasicrystals. After a short introduction to the basic concepts
of quasiperiodicity, we consider the experimental transport properties of
electrical conductivity with particular focus on the effect of temperature,
magnetic field and defects. Then, we present some heuristic approaches that
tend to give a coherent view of different, and to some extent complementary,
transport mechanisms in quasicrystals. Numerical results are also presented and
in particular the evaluation of the linear response Kubo-Greenwood formula of
conductivity in quasiperiodic systems in presence of disorder.Comment: Latex, 28 pages, Journ. of Math. Phys., Vol38 April 199
Quasi-elastic neutron scattering in the high-field phase of a Haldane antiferromagnet
Inelastic neutron scattering experiments on the Haldane-gap quantum
antiferromagnet NDMAP are performed in magnetic fields below and above the
critical field Hc at which the gap closes. Quasi-elastic neutron scattering is
found for H>Hc indicating topological excitations in the high field phase.Comment: Added to discussion section. v2: Updated figure
Temperature Variation in the Cluster of Galaxies Abell 115 Studied with ASCA
Abell 115 exhibits two distinct peaks in the surface brightness distribution.
ASCA observation shows a significant temperature variation in this cluster,
confirmed by a hardness ratio analysis and spectral fits. A linking region
between main and sub clusters shows a high temperature compared with other
regions. Two possibilities are examined as the cause of the temperature
variation: cooling flows in the main cluster and a shock heating due to the
collision of the subcluster into the main system. Spectral fits with cooling
flow models to the main-cluster data show a mass-deposition rate less than 419
solar-mass/yr. Temperatures in the main cluster, the linking region, and the
subcluster are estimated by correcting for the effects of X-ray telescope
response as 4.9 (+0.7/-0.6), 11 (+12/-4), and 5.2 (+1.4/-1.0) keV,
respectively. The high temperature in the linking region implies that Abell 115
is indeed a merger system, with possible contribution from cooling flows on the
temperature structure.Comment: 23 pages, including 7 Postscript figures, accepted for publication in
Ap
Analysis of atmospheric neutrino oscillations in three-flavor neutrinos
We analyze the atmospheric neutrino experiments of Super-Kamiokande (830-920
live days) using the three-flavor neutrino framework with the mass hierarchy
m_1 nearly equal m_2 << m_3. We study the sub-GeV, multi- GeV neutrinos and
upward through-going and stopping muons zenith angle distributions taking
account of the Earth matter effects thoroughly. We obtain the allowed regions
of mass and mixing parameters Delm^2_{23}, theta_{13} and theta_{23}.
Delm^2_{23} is restricted to 0.002-0.01eV^2 and theta_{13}<13degrees,
35degrees<theta_{23}<55degrees in 90% C.L. For theta_{12}, there is no
difference between the large angle solar neutrino solution and small one. From
chi^2 fit, the minimum chi^2=55(54DOF) is obtained at
Delm^2_{23}=4x10^(-3)eV^2, theta_{13}=10degrees and theta_{23} =45degrees.Comment: 16 pages, 3 figures, LaTe
Resolved 24.5 micron emission from massive young stellar objects
Massive young stellar objects (MYSO) are surrounded by massive dusty
envelopes. Our aim is to establish their density structure on scales of ~1000
AU, i.e. a factor 10 increase in angular resolution compared to similar studies
performed in the (sub)mm. We have obtained diffraction-limited (0.6") 24.5
micron images of 14 well-known massive star formation regions with
Subaru/COMICS. The images reveal the presence of discrete MYSO sources which
are resolved on arcsecond scales. For many sources, radiative transfer models
are capable of satisfactorily reproducing the observations. They are described
by density powerlaw distributions (n(r) ~ r^(-p)) with p = 1.0 +/-0.25. Such
distributions are shallower than those found on larger scales probed with
single-dish (sub)mm studies. Other sources have density laws that are
shallower/steeper than p = 1.0 and there is evidence that these MYSOs are
viewed near edge-on or near face-on, respectively. The images also reveal a
diffuse component tracing somewhat larger scale structures, particularly
visible in the regions S140, AFGL 2136, IRAS 20126+4104, Mon R2, and Cep A. We
thus find a flattening of the MYSO envelope density law going from ~10 000 AU
down to scales of ~1000 AU. We propose that this may be evidence of rotational
support of the envelope (abridged).Comment: 21 pages, accepted for A&
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