2,951 research outputs found
OT 060420: A Seemingly Optical Transient Recorded by All-Sky Cameras
We report on a ~5th magnitude flash detected for approximately 10 minutes by
two CONCAM all-sky cameras located in Cerro Pachon - Chile and La Palma -
Spain. A third all-sky camera, located in Cerro Paranal - Chile did not detect
the flash, and therefore the authors of this paper suggest that the flash was a
series of cosmic-ray hits, meteors, or satellite glints. Another proposed
hypothesis is that the flash was an astronomical transient with variable
luminosity. In this paper we discuss bright optical transient detection using
fish-eye all-sky monitors, analyze the apparently false-positive optical
transient, and propose possible causes to false optical transient detection in
all-sky cameras.Comment: 7 figures, 3 tables, accepted PAS
Localization properties of lattice fermions with plaquette and improved gauge actions
We determine the location of the mobility edge in the spectrum of
the hermitian Wilson operator in pure-gauge ensembles with plaquette, Iwasaki,
and DBW2 gauge actions. The results allow mapping a portion of the (quenched)
Aoki phase diagram. We use Green function techniques to study the localized and
extended modes. Where we characterize the localized modes in
terms of an average support length and an average localization length, the
latter determined from the asymptotic decay rate of the mode density. We argue
that, since the overlap operator is commonly constructed from the Wilson
operator, its range is set by the value of for the Wilson
operator. It follows from our numerical results that overlap simulations
carried out with a cutoff of 1 GeV, even with improved gauge actions, could be
afflicted by unphysical degrees of freedom as light as 250 MeV.Comment: RevTeX, 37 pages, 10 figures. Some textual changes. Final for
Fourier-based Function Secret Sharing with General Access Structure
Function secret sharing (FSS) scheme is a mechanism that calculates a
function f(x) for x in {0,1}^n which is shared among p parties, by using
distributed functions f_i:{0,1}^n -> G, where G is an Abelian group, while the
function f:{0,1}^n -> G is kept secret to the parties. Ohsawa et al. in 2017
observed that any function f can be described as a linear combination of the
basis functions by regarding the function space as a vector space of dimension
2^n and gave new FSS schemes based on the Fourier basis. All existing FSS
schemes are of (p,p)-threshold type. That is, to compute f(x), we have to
collect f_i(x) for all the distributed functions. In this paper, as in the
secret sharing schemes, we consider FSS schemes with any general access
structure. To do this, we observe that Fourier-based FSS schemes by Ohsawa et
al. are compatible with linear secret sharing scheme. By incorporating the
techniques of linear secret sharing with any general access structure into the
Fourier-based FSS schemes, we show Fourier-based FSS schemes with any general
access structure.Comment: 12 page
Edge-weighting of gene expression graphs
In recent years, considerable research efforts have been directed to micro-array technologies and their role in providing simultaneous information on expression profiles for thousands of genes. These data, when subjected to clustering and classification procedures, can assist in identifying patterns and providing insight on biological processes. To understand the properties of complex gene expression datasets, graphical representations can be used. Intuitively, the data can be represented in terms of a bipartite graph, with weighted edges corresponding to gene-sample node couples in the dataset. Biologically meaningful subgraphs can be sought, but performance can be influenced both by the search algorithm, and, by the graph-weighting scheme and both merit rigorous investigation. In this paper, we focus on edge-weighting schemes for bipartite graphical representation of gene expression. Two novel methods are presented: the first is based on empirical evidence; the second on a geometric distribution. The schemes are compared for several real datasets, assessing efficiency of performance based on four essential properties: robustness to noise and missing values, discrimination, parameter influence on scheme efficiency and reusability. Recommendations and limitations are briefly discussed
Before sailing on a domain-wall sea
We discuss the very different roles of the valence-quark and the sea-quark
residual masses ( and ) in dynamical domain-wall fermions
simulations. Focusing on matrix elements of the effective weak hamiltonian
containing a power divergence, we find that can be a source of a
much bigger systematic error. To keep all systematic errors due to residual
masses at the 1% level, we estimate that one needs
and , at a lattice spacing fm. The
practical implications are that (1) optimal use of computer resources calls for
a mixed scheme with different domain-wall fermion actions for the valence and
sea quarks; (2) better domain-wall fermion actions are needed for both the sea
and the valence sectors.Comment: latex, 25 pages. Improved discussion in appendix, including
correction of some technical mistakes; ref. adde
Mobility edge in lattice QCD
We determine the location of the mobility edge in the spectrum of
the hermitian Wilson operator on quenched ensembles. We confirm a theoretical
picture of localization proposed for the Aoki phase diagram. When
we also determine some key properties of the localized eigenmodes with
eigenvalues . Our results lead to simple tests for the
validity of simulations with overlap and domain-wall fermions.Comment: revtex, 4 pages, 1 figure, minor change
Comment on "Chiral anomalies and rooted staggered fermions"
In hep-lat/0701018, Creutz claims that the rooting trick used in simulations
of staggered fermions to reduce the number of tastes misses key physics
whenever the desired theory has an odd number of continuum flavors, and uses
this argument to call into question the rooting trick in general. Here we show
that his argument fails as the continuum limit is approached, and therefore
does not imply any problem for staggered simulations. We also show that the
cancellations necessary to restore unitarity in physical correlators in the
continuum limit are a straightforward consequence of the restoration of taste
symmetry.Comment: 11 pages, version 3 (4/13/07): Revisions to correspond to Creutz's
latest posting, including a change in the title. Version to appear in Physics
Letters
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