354 research outputs found
Suffix Tree Characterization of Maximal Motifs in Biological Sequences
Finding motifs in biological sequences is one of the most intriguing problems
for string algorithms designers as it is necessary to deal with approximations and this complicates the problem.
Existing algorithms run in time linear with the input size. Nevertheless, the output
size can be very large due to the approximation.
This makes the output often unreadable, next to slowing down the inference
itself. Since only a subset of the motifs, i.e. the \emph{maximal} motifs, could be
enough to give the information of all of them, in this paper, we aim at removing
such redundancy. We define notions of maximality that we characterize in the
suffix tree data structure. Given that this is used by a whole class of motifs
extraction tools, we show how these tools can be modified to include the maximality
requirement on the fly without changing the asymptotical complexity
Statistical Inspired Parton Distributions and the Violation of QPM Sum Rules
A quantum statistical parametrization of parton distributions has been
considered. In this framework, the exclusion Pauli principle connects the
violation of the Gottfried sum rule with the Ellis and Jaffe one, and implies a
defect in the Bjorken sum rule. However, in terms of standard parametrizations
of the polarized distributions a good description of the data is obtained once
a large gluon polarization is provided. Interestingly, in this description
there is no violation of the Bjorken sum rule.Comment: 10 pages, LateX + 15 figures, Talk given at ``Hadrons 96'' Workshop,
Novy Svet (CRIMEA), June 9-1
Even faster elastic-degenerate string matching via fast matrix multiplication
An elastic-degenerate (ED) string is a sequence of n sets of strings of total length N, which was recently proposed to model a set of similar sequences. The ED string matching (EDSM) problem is to find all occurrences of a pattern of length m in an ED text. The EDSM problem has recently received some attention in the combinatorial pattern matching community, and an O(nm1.5 â(log m) + N)-time algorithm is known [Aoyama et al., CPM 2018]. The standard assumption in the prior work on this question is that N is substantially larger than both n and m, and thus we would like to have a linear dependency on the former. Under this assumption, the natural open problem is whether we can decrease the 1.5 exponent in the time complexity, similarly as in the related (but, to the best of our knowledge, not equivalent) word break problem [Backurs and Indyk, FOCS 2016].Our starting point is a conditional lower bound for the EDSM problem. We use the popular combinatorial Boolean matrix multiplication (BMM) conjecture stating that there is no truly subcubic combinatorial algorithm for BMM [Abboud and Williams, FOCS 2014]. By designing an appropriate reduction we show that a combinatorial algorithm solving the EDSM problem in O(nm1.5ââ + N) time, for any â > 0, refutes this conjecture. Of course, the notion of combinatorial algorithms is not clearly defined, so our reduction should be understood as an indication that decreasing the exponent requires fast matrix multiplication.Two standard tools used in algorithms on strings are string periodicity and fast Fourier transform. Our main technical contribution is that we successfully combine these tools with fast matrix multiplication to design a non-combinatorial O(nm1.381 + N)-time algorithm for EDSM. To the best of our knowledge, we are the first to do so.</p
A proton-recoil track imaging system for fast neutrons: the RIPTIDE detector
Fast neutron detection is often based on the neutron-proton elastic
scattering reaction: the ionization caused by recoil protons in a hydrogenous
material constitutes the basic information for the design and development of a
class of neutron detectors. Although experimental techniques have continuously
improved, proton-recoil track imaging remains still at the frontier of
n-detection systems, due to the high photon sensitivity required. Several
state-of-the-art approaches for neutron tracking by using n-p single and double
scattering - referred to as Recoil Proton Track Imaging (RPTI) - can be found
in the literature. So far, they have showed limits in terms of detection
efficiency, complexity, cost, and implementation. In order to address some of
these deficiencies, we have proposed RIPTIDE a novel recoil-proton track
imaging detector in which the light output produced by a fast scintillator is
used to perform a complete reconstruction in space and time of the interaction
events. The proposed idea is viable thanks to the dramatic advances in low
noise and single photon counting achieved in the last decade by new scientific
CMOS cameras as well as pixel sensors, like Timepix or MIMOSIS. In this
contribution, we report the advances on the RIPTIDE concept: Geant4 Monte Carlo
simulations, light collection tests as well as state-of-the-art approach to
image readout, processing and fast analysis.Comment: proceeding of the 23rd International Workshop on Radiation Imaging
Detectors, IWoRID 2022, 26-30 June 2022, Riva del Garda (TN), Ital
Neutrino masses and mixings in a seesaw framework
Assuming the seesaw mechanism for hierarchical neutrino masses, we calculate
the heavy neutrino masses under the hypotheses that the mixing in the Dirac
leptonic sector is similar to the quark mixing () and that
or , where is the Dirac mass matrix of
neutrinos. As a result we find that for the vacuum
oscillation solution of the solar neutrino problem leads to a scale for the
heavy neutrino mass well above the unification scale, while for the MSW
solutions there is agreement with this scale. For the vacuum
solution is consistent with the unification scale, and the MSW solutions with
an intermediate scale. The mass of the lightest heavy neutrino can be as small
as GeV.Comment: 13 pages RevTex, no figures. Revised versio
Upper Bounds on the Neutrino-Nucleon Inelastic Cross Section
Extraterrestrial neutrinos can initiate deeply developing air showers, and
those that traverse the atmosphere unscathed may produce cascades in the ice or
water. Up to now, no such events have been observed. This can be translated
into upper limits on the diffuse neutrino flux. On the other hand, the
observation of cosmic rays with primary energies > 10^{10} GeV suggests that
there is a guaranteed flux of cosmogenic neutrinos, arising from the decay of
charged pions (and their muon daughters) produced in proton interactions with
the cosmic microwave background. In this work, armed with these cosmogenic
neutrinos and the increased exposure of neutrino telescopes we bring up-to-date
model-independent upper bounds on the neutrino-nucleon inelastic cross section.
Uncertainties in the cosmogenic neutrino flux are discussed and taken into
account in our analysis. The prospects for improving these bounds with the
Pierre Auger Observatory are also estimated. The unprecedented statistics to be
collected by this experiment in 6 yr of operation will probe the
neutrino-nucleon inelastic cross section at the level of Standard Model
predictions.Comment: To be published in JCA
Early-universe constraints on a time-varying fine structure constant
Higher-dimensional theories have the remarkable feature of predicting a time
(and hence redshift) dependence of the `fundamental' four dimensional constants
on cosmological timescales. In this paper we update the bounds on a possible
variation of the fine structure constant alpha at the time of BBN (z =10^10)
and CMB (z=10^3). Using the recently-released high-resolution CMB anisotropy
data and the latest estimates of primordial abundances of 4He and D, we do not
find evidence for a varying alpha at more than one-sigma level at either epoch.Comment: 5 pages, 1 figure, minor misprints corrected, references added. The
analysis has been updated using new BOOMERanG and DASI data on CMB anisotrop
Big Bang Nucleosynthesis and Particle Dark Matter
We review how our current understanding of the light element synthesis during
the Big Bang Nucleosynthesis era may help shed light on the identity of
particle dark matter.Comment: a mini-review for the NJP special issue on dark matte
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