On a Speculated Relation Between Chv\'atal-Sankoff Constants of Several Sequences

It is well known that, when normalized by n, the expected length of a longest common subsequence of d sequences of length n over an alphabet of size sigma converges to a constant gamma_{sigma,d}. We disprove a speculation by Steele regarding a possible relation between gamma_{2,d} and gamma_{2,2}. In order to do that we also obtain new lower bounds for gamma_{sigma,d}, when both sigma and d are small integers.Comment: 13 pages. To appear in Combinatorics, Probability and Computin

Modeling Two Dimensional Magnetic Domain Patterns

Two-dimensional magnetic garnets exhibit complex and fascinating magnetic domain structures, like stripes, labyrinths, cells and mixed states of stripes and cells. These patterns do change in a reversible way when the intensity of an externally applied magnetic field is varied. The main objective of this contribution is to present the results of a model that yields a rich pattern structure that closely resembles what is observed experimentally. Our model is a generalized two-dimensional Ising-like spin-one Hamiltonian with long-range interactions, which also incorporates anisotropy and Zeeman terms. The model is studied numerically, by means of Monte Carlo simulations. Changing the model parameters stripes, labyrinth and/or cellular domain structures are generated. For a variety of cases we display the patterns, determine the average size of the domains, the ordering transition temperature, specific heat, magnetic susceptibility and hysteresis cycle. Finally, we examine the reversibility of the pattern evolution under variations of the applied magnetic field. The results we obtain are in good qualitative agreement with experiment.Comment: 8 pages, 12 figures, submitted to Phys. Rev.

Magnetic reordering in the vicinity of a ferromagnetic/antiferromagnetic interface

The magnetic arrangement in the vicinity of the interface between a ferromagnet and an antiferromagnet is investigated, in particular its dependence on the exchange couplings and the temperature. Applying a Heisenberg model, both sc(001) and fcc(001) lattices are considered and solved by a mean field approximation. Depending on the parameter values a variety of different magnetic configurations emerge. Usually the subsystem with the larger ordering temperature induces a magnetic order into the other one (magnetic proximity effect). With increasing temperature a reorientation of the magnetic sublattices is obtained. For coupled sc(001) systems both FM and AFM films are disturbed from their collinear magnetic order, hence exhibit a similar behavior. This symmetry is absent for fcc(001) films which, under certain circumstances, may exhibit two different critical temperatures. Analytical results are derived for simple bilayer systems.Comment: accepted for publication in Eur. Phys. J.

Metastable Random Field Ising model with exchange enhancement: a simple model for Exchange Bias

We present a simple model that allows hysteresis loops with exchange bias to be reproduced. The model is a modification of the T=0 random field Ising model driven by an external field and with synchronous local relaxation dynamics. The main novelty of the model is that a certain fraction f of the exchange constants between neighbouring spins is enhanced to a very large value J_E. The model allows the dependence of the exchange bias and other properties of the hysteresis loops to be analyzed as a function of the parameters of the model: the fraction f of enhanced bonds, the amount of the enhancement J_E and the amount of disorder which is controlled by the width sigma of the Gaussian distribution of the random fields.Comment: 8 pages, 11 figure

Performance factors for successful business incubators in Indonesian public universities

Measuring the performance of business processes is already a main concern for both faculty and enterprise players, since organizations are motivated to reach the productivity stage. Employing a performance achievement framework for the relationship between business incubator success factors will guarantee connection with commercial schemes, which support a high level of performance indicators in successful business incubator models. This research employs a quantitative approach, with the data analyzed using the IBM SPSS version 23 and Smart PLS version 3 statistical software packages. Employing a sample of 95 incubator managers from 19 universities which geographically located in Indonesia, it is shown that the image of business incubator factors has a positive effect on incubator performance. The study investigates the relationship between incubator performance and business incubator success factors in Indonesia. It was found that IT, as part of the business incubators’ facets/abilities, partially supports their performance; that the entry criteria directly support the performance of the incubators; that mentoring networks also support the performance, with good infrastructure systems as a moderating factor; that funding supports the performance of business incubators, also with good infrastructure systems as a moderating factor; and that university regulations and government support and protection enhance the performance of business incubators, with credits and rewards as a moderating factor. In addition, a variety of indicators from the local context affiliate positively to promote a community that highlighted the incubators’ strategies.N/

Expected length of the longest common subsequence for large alphabets

We consider the length L of the longest common subsequence of two randomly uniformly and independently chosen n character words over a k-ary alphabet. Subadditivity arguments yield that the expected value of L, when normalized by n, converges to a constant C_k. We prove a conjecture of Sankoff and Mainville from the early 80's claiming that C_k\sqrt{k} goes to 2 as k goes to infinity.Comment: 14 pages, 1 figure, LaTe

In-plane magnetic reorientation in coupled ferro- and antiferromagnetic thin films

By studying coupled ferro- (FM) and antiferromagnetic (AFM) thin film systems, we obtain an in-plane magnetic reorientation as a function of temperature and FM film thickness. The interlayer exchange coupling causes a uniaxial anisotropy, which may compete with the intrinsic anisotropy of the FM film. Depending on the latter the total in-plane anisotropy of the FM film is either enhanced or reduced. Eventually a change of sign occurs, resulting in an in-plane magnetic reorientation between a collinear and an orthogonal magnetic arrangement of the two subsystems. A canted magnetic arrangement may occur, mediating between these two extremes. By measuring the anisotropy below and above the N\'eel temperature the interlayer exchange coupling can be determined. The calculations have been performed with a Heisenberg-like Hamiltonian by application of a two-spin mean-field theory.Comment: 4 pages, 4 figure

Two-stage magnetization reversal in exchange biased bilayers

MnF2/Fe bilayers exhibit asymmetric magnetization reversal that occurs by coherent rotation on one side of the loop and by nucleation and propagation of domain walls on the other side of the loop. Here, we show by polarized neutron reflectometry, magnetization, and magnetotransport measurements that for samples with good crystalline "quality" the rotation is a two-stage process, due to coherent rotation to a stable state perpendicular to the cooling field direction. The result is remarkably asymmetrically shaped hysteresis loops

Combined XPS and TPD study of oxygen-functionalized carbon nanofibers grown on sintered metal fibers

A novel composite material consisting of carbon nanofibers (CNF) grown on sintered metal fibers (SMF) filters was modified by H2O2 or plasma-generated O3. Coupling TPD and XPS techniques in the same UHV apparatus allowed the direct correlation between the nature of the created O-functional groups and their evolution as CO and CO2 upon heating. The two oxidative treatments yielded different distributions of O-containing groups. The relative contribution of oxidized carbon was very low in the C1s region, so the functional groups were better analyzed in the O1s region. The quantification of the released oxygen by integration of the TPD CO, CO2 and H2O spectra, compared with the intensity loss of the XPS O1s spectra showed a good agreement. In order to fit the data adequately, the set of O1s spectra was decomposed in at least four peaks for the differently activated samples. Finally, it was shown that functional groups formed by H2O2-treatment (mostly non-phenolic OH groups) are thermally more stable than the ones formed by O3-treatment. The latter treatment increases the concentration of carboxylic functionalities, which decomposes at temperatures < 800 K; O3-activated CNF therefore should show a more pronounced acidic behavior