373 research outputs found
Finding All Solutions of Equations in Free Groups and Monoids with Involution
The aim of this paper is to present a PSPACE algorithm which yields a finite
graph of exponential size and which describes the set of all solutions of
equations in free groups as well as the set of all solutions of equations in
free monoids with involution in the presence of rational constraints. This
became possible due to the recently invented emph{recompression} technique of
the second author.
He successfully applied the recompression technique for pure word equations
without involution or rational constraints. In particular, his method could not
be used as a black box for free groups (even without rational constraints).
Actually, the presence of an involution (inverse elements) and rational
constraints complicates the situation and some additional analysis is
necessary. Still, the recompression technique is general enough to accommodate
both extensions. In the end, it simplifies proofs that solving word equations
is in PSPACE (Plandowski 1999) and the corresponding result for equations in
free groups with rational constraints (Diekert, Hagenah and Gutierrez 2001). As
a byproduct we obtain a direct proof that it is decidable in PSPACE whether or
not the solution set is finite.Comment: A preliminary version of this paper was presented as an invited talk
at CSR 2014 in Moscow, June 7 - 11, 201
Polarization studies of Rotating Radio Transients
We study the polarization properties of 22 known rotating radio transients
(RRATs) with the 64-m Parkes radio telescope and present the Faraday rotation
measures (RMs) for the 17 with linearly polarized flux exceeding the off-pulse
noise by 3. Each RM was estimated using a brute-force search over trial
RMs that spanned the maximum measurable range (in steps of 1 ), followed by an
iterative refinement algorithm. The measured RRAT RMs are in the range |RM|
to rad m with an average linear polarization
fraction of per cent. Individual single pulses are observed to be up
to 100 per cent linearly polarized. The RMs of the RRATs and the corresponding
inferred average magnetic fields (parallel to the line-of-sight and weighted by
the free electron density) are observed to be consistent with the Galactic
plane pulsar population. Faraday rotation analyses are typically performed on
accumulated pulsar data, for which hundreds to thousands of pulses have been
integrated, rather than on individual pulses. Therefore, we verified the
iterative refinement algorithm by performing Monte Carlo simulations of
artificial single pulses over a wide range of S/N and RM. At and above a S/N of
17 in linearly polarized flux, the iterative refinement recovers the simulated
RM value 100 per cent of the time with a typical mean uncertainty of
rad m. The method described and validated here has also been
successfully used to determine reliable RMs of several fast radio bursts (FRBs)
discovered at Parkes.Comment: Submitted to MNRAS, 10 pages, 6 figure
Investigation of octupole vibrational states in 150Nd via inelastic proton scattering (p,p'g)
Octupole vibrational states were studied in the nucleus
via inelastic proton scattering with \unit[10.9]{MeV} protons which are an
excellent probe to excite natural parity states. For the first time in
, both the scattered protons and the rays were
detected in coincidence giving the possibility to measure branching ratios in
detail. Using the coincidence technique, the ratios of the decaying
transitions for 10 octupole vibrational states and other negative-parity states
to the yrast band were determined and compared to the Alaga rule. The positive
and negative-parity states revealed by this experiment are compared with
Interacting Boson Approximation (IBA) calculations performed in the (spdf)
boson space. The calculations are found to be in good agreement with the
experimental data, both for positive and negative-parity states
Words with the Maximum Number of Abelian Squares
An abelian square is the concatenation of two words that are anagrams of one
another. A word of length can contain distinct factors that
are abelian squares. We study infinite words such that the number of abelian
square factors of length grows quadratically with .Comment: To appear in the proceedings of WORDS 201
Distinction between the Poole-Frenkel and tunneling models of electric field-stimulated carrier emission from deep levels in semiconductors
The enhancement of the emission rate of charge carriers from deep-level defects in electric field is routinely used to determine the charge state of the defects. However, only a limited number of defects can be satisfactorily described by the Poole-Frenkel theory. An electric field dependence different from that expected from the Poole-Frenkel theory has been repeatedly reported in the literature, and no unambiguous identification of the charge state of the defect could be made. In this article, the electric field dependencies of emission of carriers from DX centers in AlxGa1-xAs:Te, Cu pairs in silicon, and Ge:Hg have been studied applying static and terahertz electric fields, and analyzed by using the models of Poole-Frenkel and phonon assisted tunneling. It is shown that phonon assisted tunneling and Poole-Frenkel emission are two competitive mechanisms of enhancement of emission of carriers, and their relative contribution is determined by the charge state of the defect and by the electric-field strength. At high-electric field strengths carrier emission is dominated by tunneling independently of the charge state of the impurity. For neutral impurities, where Poole-Frenkel lowering of the emission barrier does not occur, the phonon assisted tunneling model describes well the experimental data also in the low-field region. For charged impurities the transition from phonon assisted tunneling at high fields to Poole-Frenkel effect at low fields can be traced back. It is suggested that the Poole-Frenkel and tunneling models can be distinguished by plotting logarithm of the emission rate against the square root or against the square of the electric field, respectively. This analysis enables one to unambiguously determine the charge state of a deep-level defect
Diode area melting single-layer parametric analysis of 316L stainless steel powder
Diode area melting (DAM) is a novel additive manufacturing process that utilises customised architectural arrays of low power laser diode emitters for high speed parallel processing of metallic powdered feedstock. The laser diodes operate at shorter laser wavelengths (808 nm) than conventional SLM fibre lasers (1064 nm) theoretically enabling more efficient energy absorption for specific materials. This investigation presents a parametric analysis of the DAM process, identifying the effect of powder characteristics, laser beam profile, laser power and scan speed on the porosity of a single-layer sample. Also presented is the effect of process energy density on melt pool depth (irradiated thermal energy penetration capable of achieving melting) on 316L stainless steel powder. An analysis of the density and the melt depth fraction of single layers is presented in order to identify the conditions that lead to the fabrication of fully dense DAM parts. Energy densities in excess of 86 J/mm3 were theorised as sufficient to enable processing of fully dense layers
Mixed-symmetry octupole and hexadecapole excitations in N=52 isotones
In addition to the well-established quadrupole mixed-symmetry states, octupole and hexadecapole excitations with mixed-symmetry character have been recently proposed for the N = 52 isotones 92Zr and 94Mo. We performed two inelastic proton-scattering experiments to study this kind of excitations in the heaviest stable N = 52 isotone 96Ru. From the combined experimental data of both experiments absolute transition strengths were extracted
Continuous flow micro-cell for electrochemical addressing of engineered bio-molecules
Abstract A micro-cell consisting of a planar array of Au working electrodes, covered by a glass reservoir (600 nl capacity), connected with perpendicular capillaries and provided with an Ag/AgCl wire reference electrode (RE) has been manufactured. Addressed on-chip immobilization and sensing of biomolecules was demonstrated by the immobilization of histidine (HIS) tagged alkaline phosphatase (AP) under continuous flow (10 l/min) conditions on the base of electrochemically deposited multilayer (EDM) of cysteamine modified by nitrilotriacetic acid (NTA). The presented method allows the immobilization of different biomolecules on the ready-to-use reservoir covered chip without needs of manual biomolecule deposition. Further on, the detection of analytes can be performed using the electrochemical measurements. Since the methods of biomolecule deposition and sensing are both electrochemical, this allows simplifying the production technology using cheaper detection instruments compared to prevailing present-day optical detection modes
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