31,720 research outputs found
Optimal locally repairable codes of distance and via cyclic codes
Like classical block codes, a locally repairable code also obeys the
Singleton-type bound (we call a locally repairable code {\it optimal} if it
achieves the Singleton-type bound). In the breakthrough work of \cite{TB14},
several classes of optimal locally repairable codes were constructed via
subcodes of Reed-Solomon codes. Thus, the lengths of the codes given in
\cite{TB14} are upper bounded by the code alphabet size . Recently, it was
proved through extension of construction in \cite{TB14} that length of -ary
optimal locally repairable codes can be in \cite{JMX17}. Surprisingly,
\cite{BHHMV16} presented a few examples of -ary optimal locally repairable
codes of small distance and locality with code length achieving roughly .
Very recently, it was further shown in \cite{LMX17} that there exist -ary
optimal locally repairable codes with length bigger than and distance
propositional to .
Thus, it becomes an interesting and challenging problem to construct new
families of -ary optimal locally repairable codes of length bigger than
.
In this paper, we construct a class of optimal locally repairable codes of
distance and with unbounded length (i.e., length of the codes is
independent of the code alphabet size). Our technique is through cyclic codes
with particular generator and parity-check polynomials that are carefully
chosen
Global Neutrino Heating in Hyperaccretion Flows
The neutrino-dominated accretion flow (NDAF) with accretion rates \dot{M} =
0.01 - 10 M_{\sun} s^{-1} is a plausible candidate for the central engine of
gamma-ray bursts (GRBs). This hyperaccretion disk is optically thin to
neutrinos in the radial direction, therefore the neutrinos produced at one
radius can travel for a long distance in the disk. Those neutrinos can thus be
absorbed with certain probability by the disk matter at the other radius and
heat the disk there. The effect of this "global neutrino heating" has been
ignored in previous works and is the focus of this paper. We find that around
the "ignition" radius r_{ign}, the global neutrino heating rate could be
comparable to or even larger than the local viscous heating rate thus must be
an important process. Two possible consequences are in order if the "global
neutrino heating" is taken into account: i) the temperature of the disk is
slightly raised and the "ignition" radius r_{ign} slightly shifts to a larger
radius, both lead to the increasing of the total neutrino flux; ii) what is
more interesting is that, the temperature of the ADAF just beyond r_{ign} may
be raised above the virial temperature thus the accretion will be suppressed.
In this case, the activity of the black hole is expected to oscillate between
an active and inactive phases. The timescale of the active phases is estimated
to be \sim 1 second. If the timescale of the inactive phase is comparable to or
less than this value, this intermittent activity may explain the slow
variability component of the GRBs. Self-consistent global calculations of NDAFs
with the "global neutrino heating" included are required in the future to more
precisely evaluate this effect.Comment: 9 pages, 5 figures; more discussions and references added; accepted
for publication in MNRA
The Weight Distributions of a Class of Cyclic Codes with Three Nonzeros over F3
Cyclic codes have efficient encoding and decoding algorithms. The decoding
error probability and the undetected error probability are usually bounded by
or given from the weight distributions of the codes. Most researches are about
the determination of the weight distributions of cyclic codes with few
nonzeros, by using quadratic form and exponential sum but limited to low
moments. In this paper, we focus on the application of higher moments of the
exponential sum to determine the weight distributions of a class of ternary
cyclic codes with three nonzeros, combining with not only quadratic form but
also MacWilliams' identities. Another application of this paper is to emphasize
the computer algebra system Magma for the investigation of the higher moments.
In the end, the result is verified by one example using Matlab.Comment: 10 pages, 3 table
Implementing a Portable Clinical NLP System with a Common Data Model - a Lisp Perspective
This paper presents a Lisp architecture for a portable NLP system, termed
LAPNLP, for processing clinical notes. LAPNLP integrates multiple standard,
customized and in-house developed NLP tools. Our system facilitates portability
across different institutions and data systems by incorporating an enriched
Common Data Model (CDM) to standardize necessary data elements. It utilizes
UMLS to perform domain adaptation when integrating generic domain NLP tools. It
also features stand-off annotations that are specified by positional reference
to the original document. We built an interval tree based search engine to
efficiently query and retrieve the stand-off annotations by specifying
positional requirements. We also developed a utility to convert an inline
annotation format to stand-off annotations to enable the reuse of clinical text
datasets with inline annotations. We experimented with our system on several
NLP facilitated tasks including computational phenotyping for lymphoma patients
and semantic relation extraction for clinical notes. These experiments
showcased the broader applicability and utility of LAPNLP.Comment: 6 pages, accepted by IEEE BIBM 2018 as regular pape
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