Tabu search for the cyclic bandwidth problem

The Cyclic Bandwidth (CB) problem for graphs consists in labeling the vertices of a guest graph G by distinct vertices of a host cycle Cn (both of order n) in such a way that the maximum distance in the cycle between adjacent vertices in G is minimized. To the best of our knowledge, this is the first research work investigating the use of metaheuristic algorithms for solving this challenging combinatorial optimization problem in the case of general graphs. In this paper a new carefully devised Tabu Search   algorithm, called TScb, for finding near-optimal solutions for the CB problem is proposed. Different possibilities for its key components and input parameter values were carefully analyzed and tuned, in order to find the combination of them offering the best quality solutions to the problem at a reasonable computational effort. Extensive experimentation was carried out, using 113 standard benchmark instances, for assessing its performance with respect to a Simulated Annealing (SAcb) implementation. The experimental results show that there exists a statistically significant performance amelioration achieved by TScb with respect toSAcb in 90 out of 113 graphs (79.646%). It was also found that our TScb algorithm attains 56 optimal solutions and establishes new better upper bounds for the other 57 instances. Furthermore, these competitive results were obtained expending reasonable computational times

FSD-HSO Optimization Algorithm for Closed Fringes Interferogram Demodulation

Due to the physical nature of the interference phenomenon, extracting the phase of an interferogram is a known sinusoidal modulation problem. In order to solve this problem, a new hybrid mathematical optimization model for phase extraction is established. The combination of frequency guide sequential demodulation and harmony search optimization algorithms is used for demodulating closed fringes patterns in order to find the phase of interferogram applications. The proposed algorithm is tested in four sets of different synthetic interferograms, finding a range of average relative error in phase reconstructions of 0.14–0.39 rad. For reference, experimental results are compared with the genetic algorithm optimization technique, obtaining a reduction in the error up to 0.1448 rad. Finally, the proposed algorithm is compared with a very known demodulation algorithm, using a real interferogram, obtaining a relative error of 1.561 rad. Results are shown in patterns with complex fringes distribution

Anomaly in Spin Excitation Spectrum of Double-Exchange Systems with Randomness

Spin excitation spectrum of the double-exchange model is studied in the presence of randomness. Spin wave approximation in the ground state shows that the randomness significantly modifies the spectrum from the cosine-like one in the pure system to that with anomalies such as broadening, anti-crossing and gap opening. The origin of anomalies is speculated to be modulation of effective ferromagnetic coupling by the Friedel oscillation. These anomalies qualitatively reproduce the spin excitation spectrum in colossal magnetoresistance manganites whose Curie temperatures are relatively low. Our results suggest that randomness control is an important notion to understand effects of the A-site substitution which has previously been understood as the bandwidth control.Comment: 4 pages including 3 figure

Crystal and magnetic structure of the La1−x_{1-x}Cax_{x}MnO3_{3} compound (x=0.8,0.85)(x=0.8,0.85)

We studied the crystal and magnetic structure of the La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound for $x=0.8$ and $x=0.85$. At T=300 K both samples are paramagnetic with crystallographic symmetry $Pnma$. At low temperatures they undergo a monoclinic distortion from orthorhombic $Pnma$-type structure with $a_p\sqrt{2}\times 2a_p\times a_p\sqrt{2}$ to a monoclinic structure with ($a_p\sqrt{2}\times 2a_p\times a_p\sqrt{2}$, $\beta=90+\epsilon\sim 91.4^{\rm o}$) and $P2_1/m$ space group below $T_N$. The onset of the structural transformation coincides with the development of the $C$-type long range antiferromagnetic order with propagation vector ${\bf k}=({1/2},0,{1/2})$. The monoclinic unit cell allowed us to determine the direction of the Mn magnetic moment with respect to the crystallographic axes: it is perpendicular to the propagation vector, ${\bf m}\perp {\bf k}=({1/2},0,{1/2})$. The amplitude of the ordered magnetic moment at $T=1.6$ K is found to be $2.53(2)$ and $2.47(2)\mu_{B}$ for $x=0.8$ and 0.85, respectively.Comment: In press (Phys. Rev B 01 Feb 2002