1,698 research outputs found
Silent MST approximation for tiny memory
In network distributed computing, minimum spanning tree (MST) is one of the
key problems, and silent self-stabilization one of the most demanding
fault-tolerance properties. For this problem and this model, a polynomial-time
algorithm with memory is known for the state model. This is
memory optimal for weights in the classic range (where
is the size of the network). In this paper, we go below this
memory, using approximation and parametrized complexity.
More specifically, our contributions are two-fold. We introduce a second
parameter~, which is the space needed to encode a weight, and we design a
silent polynomial-time self-stabilizing algorithm, with space . In turn, this allows us to get an approximation algorithm for the problem,
with a trade-off between the approximation ratio of the solution and the space
used. For polynomial weights, this trade-off goes smoothly from memory for an -approximation, to memory for exact solutions,
with for example memory for a 2-approximation
The zero exemplar distance problem
Given two genomes with duplicate genes, \textsc{Zero Exemplar Distance} is
the problem of deciding whether the two genomes can be reduced to the same
genome without duplicate genes by deleting all but one copy of each gene in
each genome. Blin, Fertin, Sikora, and Vialette recently proved that
\textsc{Zero Exemplar Distance} for monochromosomal genomes is NP-hard even if
each gene appears at most two times in each genome, thereby settling an
important open question on genome rearrangement in the exemplar model. In this
paper, we give a very simple alternative proof of this result. We also study
the problem \textsc{Zero Exemplar Distance} for multichromosomal genomes
without gene order, and prove the analogous result that it is also NP-hard even
if each gene appears at most two times in each genome. For the positive
direction, we show that both variants of \textsc{Zero Exemplar Distance} admit
polynomial-time algorithms if each gene appears exactly once in one genome and
at least once in the other genome. In addition, we present a polynomial-time
algorithm for the related problem \textsc{Exemplar Longest Common Subsequence}
in the special case that each mandatory symbol appears exactly once in one
input sequence and at least once in the other input sequence. This answers an
open question of Bonizzoni et al. We also show that \textsc{Zero Exemplar
Distance} for multichromosomal genomes without gene order is fixed-parameter
tractable if the parameter is the maximum number of chromosomes in each genome.Comment: Strengthened and reorganize
Neutrino-Nucleus Reactions and Muon Capture in 12C
The neutrino-nucleus cross section and the muon capture rate are discussed
within a simple formalism which facilitates the nuclear structure calculations.
The corresponding formulae only depend on four types of nuclear matrix
elements, which are currently used in the nuclear beta decay. We have also
considered the non-locality effects arising from the velocity-dependent terms
in the hadronic current. We show that for both observables in 12C the higher
order relativistic corrections are of the order of ~5 only, and therefore do
not play a significant role. As nuclear model framework we use the projected
QRPA (PQRPA) and show that the number projection plays a crucial role in
removing the degeneracy between the proton-neutron two quasiparticle states at
the level of the mean field. Comparison is done with both the experimental data
and the previous shell model calculations. Possible consequences of the present
study on the determination of the neutrino oscillation
probability are briefly addressed.Comment: 29 pages, 6 figures, Revtex4. Several changes were made to the
previous manuscript, the results and final conclusions remain unalterable. It
has been accepted for publication as a Regular Article in Physical Review
Voltage controlled terahertz transmission through GaN quantum wells
We report measurements of radiation transmission in the 0.220--0.325 THz
frequency domain through GaN quantum wells grown on sapphire substrates at room
and low temperatures. A significant enhancement of the transmitted beam
intensity with the applied voltage on the devices under test is found. For a
deeper understanding of the physical phenomena involved, these results are
compared with a phenomenological theory of light transmission under electric
bias relating the transmission enhancement to changes in the differential
mobility of the two-dimensional electron gas
Isoscalar g Factors of Even-Even and Odd-Odd Nuclei
We consider T=0 states in even-even and odd-odd N=Z nuclei. The g factors
that emerge are isoscalar. We find that the single j shell model gives simple
expressions for these g factors which for even-even nuclei are suprisingly
close to the collective values for K=0 bands. The g factors of many 2+ in
even-even nuclei and 1+ and 3+ states in odd-odd nuclei have g factors close to
0.5
Hyperfine Structure Constants for Eu Isotopes: Is The Empirical Formula of HFS Anomaly Universal ?
We calculate the hyperfine structure constant for the Eu isotopes with shell
model wave functions. The calculated results are compared with those predicted
by the Moskowitz-Lombardi (M-L) empirical formula. It turns out that the two
approaches give the very different behaviors of the hfs constants in the
isotope dependence. This should be easily measured by experiment, which may
lead to the universality check of the M-L formula.Comment: 18 pages, Latex, two figure
Counting, generating and sampling tree alignments
Pairwise ordered tree alignment are combinatorial objects that appear in RNA
secondary structure comparison. However, the usual representation of tree
alignments as supertrees is ambiguous, i.e. two distinct supertrees may induce
identical sets of matches between identical pairs of trees. This ambiguity is
uninformative, and detrimental to any probabilistic analysis.In this work, we
consider tree alignments up to equivalence. Our first result is a precise
asymptotic enumeration of tree alignments, obtained from a context-free grammar
by mean of basic analytic combinatorics. Our second result focuses on
alignments between two given ordered trees and . By refining our grammar
to align specific trees, we obtain a decomposition scheme for the space of
alignments, and use it to design an efficient dynamic programming algorithm for
sampling alignments under the Gibbs-Boltzmann probability distribution. This
generalizes existing tree alignment algorithms, and opens the door for a
probabilistic analysis of the space of suboptimal RNA secondary structures
alignments.Comment: ALCOB - 3rd International Conference on Algorithms for Computational
Biology - 2016, Jun 2016, Trujillo, Spain. 201
Identification of TMEM206 proteins as pore of PAORAC/ASOR acid-sensitive chloride channels
Acid-sensing ion channels have important functions in physiology and pathology, but the molecular composition of acid-activated chloride channels had remained unclear. We now used a genome-wide siRNA screen to molecularly identify the widely expressed acid-sensitive outwardly-rectifying anion channel PAORAC/ASOR. ASOR is formed by TMEM206 proteins which display two transmembrane domains (TMs) and are expressed at the plasma membrane. Ion permeation-changing mutations along the length of TM2 and at the end of TM1 suggest that these segments line ASOR's pore. While not belonging to a gene family, TMEM206 has orthologs in probably all vertebrates. Currents from evolutionarily distant orthologs share activation by protons, a feature essential for ASOR's role in acid-induced cell death. TMEM206 defines a novel class of ion channels. Its identification will help to understand its physiological roles and the diverse ways by which anion-selective pores can be formed
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