38,041 research outputs found
Classifications of the Host Galaxies of Supernovae, Set II
Classifications on the DDO system are given for an additional 231 host
galaxies of supernovae that have been discovered during the course of the Lick
Observatory Supernova Search with the Katzman Automatic Imaging Telescope
(KAIT). This brings the total number of hosts of supernovae discovered (or
independently rediscovered) by KAIT, which have so far been classified on a
homogeneous system, to 408. The probability that SNe Ia and SNe II have a
different distribution of host galaxy Hubble types is found to be 99.7%. A
significant difference is also found between the distributions of the host
galaxies of SNe Ia and of SNe Ibc (defined here to include SNe Ib, Ib/c, and
Ic). However, no significant difference is detected between the frequency
distributions of the host galaxies of SNe II and SNe IIn. This suggests that
SNe IIn are generally not SNe Ia embedded in circumstellar material that are
masquerading as SNe II. Furthermore, no significant difference is found between
the distribution of the Hubble types of the hosts of SNe Ibc and of SNe II.
Additionally, SNe II-P and SNe II-L are found to occur among similar stellar
populations. The ratio of the number of SNe Ia-pec to normal SNe Ia appears to
be higher in early-type galaxies than it is in galaxies of later morphological
types. This suggests that the ancestors of SNe Ia-pec may differ systematically
in age or composition from the progenitors of normal SNe Ia. Unexpectedly, five
SNe of Types Ib/c, II, and IIn (all of which are thought to have massive
progenitors) are found in host galaxies that are nominally classified as types
E and S0. However, in each case the galaxy classification is uncertain, or
newly inspected images show evidence suggesting a later classification
(abridged) ...Comment: Accepted for publishing in PAS
Stochastically perturbed flows: Delayed and interrupted evolution
We present analytical expressions for the time-dependent and stationary
probability distributions corresponding to a stochastically perturbed
one-dimensional flow with critical points, in two physically relevant
situations: delayed evolution, in which the flow alternates with a quiescent
state in which the variate remains frozen at its current value for random
intervals of time; and interrupted evolution, in which the variate is also
re-set in the quiescent state to a random value drawn from a fixed
distribution. In the former case, the effect of the delay upon the first
passage time statistics is analyzed. In the latter case, the conditions under
which an extended stationary distribution can exist as a consequence of the
competition between an attractor in the flow and the random re-setting are
examined. We elucidate the role of the normalization condition in eliminating
the singularities arising from the unstable critical points of the flow, and
present a number of representative examples. A simple formula is obtained for
the stationary distribution and interpreted physically. A similar
interpretation is also given for the known formula for the stationary
distribution in a full-fledged dichotomous flow.Comment: 27 pages; no figures. Submitted to Stochastics and Dynamic
Optical conductivity in A3C60 (A=K, Rb)
We study the optical conductivity in A3C60 (A =K, Rb). The effects of the
electron-phonon interaction is included to lowest order in the coupling
strength lambda. It is shown that this leads to a narrowing of the Drude peak
by a factor 1+lambda and a transfer of weight to a mid-infrared peak at
somewhat larger energies than the phonon energy. Although this goes in the
right direction, it is not sufficient to describe experiment.Comment: 5 pages, revtex, 2 figures more information at
http://librix.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Orbital-Peierls State in NaTiSi2O6
Does the quasi one-dimensional titanium pyroxene NaTiSi2O6 exhibit the novel
{\it orbital-Peierls} state? We calculate its groundstate properties by three
methods: Monte Carlo simulations, a spin-orbital decoupling scheme and a
mapping onto a classical model. The results show univocally that for the spin
and orbital ordering to occur at the same temperature --an experimental
observation-- the crystal field needs to be small and the orbitals are active.
We also find that quantum fluctuations in the spin-orbital sector drive the
transition, explaining why canonical bandstructure methods fail to find it. The
conclusion that NaTiSi2O6 shows an orbital-Peierls transition is therefore
inevitable.Comment: 4 pages, 3 figure
Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177
supernovae (SNe) that have been discovered since 1997 during the course of the
Lick Observatory Supernova Search with the Katzman Automatic Imaging Telescope.
Whereas SNe Ia occur in all galaxy types, it is found, at a high level of
statistical confidence, that SNe Ib, Ic, and II are strongly concentrated in
late-type galaxies. However, attention is drawn to a possible exception
provided by SN 2001I. This SN IIn occurred in the E2 galaxy UGC 2836, which was
not expected to harbor a massive young supernova progenitor.Comment: Accepted to be published in PAS
Which graph states are useful for quantum information processing?
Graph states are an elegant and powerful quantum resource for measurement
based quantum computation (MBQC). They are also used for many quantum protocols
(error correction, secret sharing, etc.). The main focus of this paper is to
provide a structural characterisation of the graph states that can be used for
quantum information processing. The existence of a gflow (generalized flow) is
known to be a requirement for open graphs (graph, input set and output set) to
perform uniformly and strongly deterministic computations. We weaken the gflow
conditions to define two new more general kinds of MBQC: uniform
equiprobability and constant probability. These classes can be useful from a
cryptographic and information point of view because even though we cannot do a
deterministic computation in general we can preserve the information and
transfer it perfectly from the inputs to the outputs. We derive simple graph
characterisations for these classes and prove that the deterministic and
uniform equiprobability classes collapse when the cardinalities of inputs and
outputs are the same. We also prove the reversibility of gflow in that case.
The new graphical characterisations allow us to go from open graphs to graphs
in general and to consider this question: given a graph with no inputs or
outputs fixed, which vertices can be chosen as input and output for quantum
information processing? We present a characterisation of the sets of possible
inputs and ouputs for the equiprobability class, which is also valid for
deterministic computations with inputs and ouputs of the same cardinality.Comment: 13 pages, 2 figure
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