Fault Localization in Multi-Threaded C Programs using Bounded Model Checking (extended version)

Software debugging is a very time-consuming process, which is even worse for multi-threaded programs, due to the non-deterministic behavior of thread-scheduling algorithms. However, the debugging time may be greatly reduced, if automatic methods are used for localizing faults. In this study, a new method for fault localization, in multi-threaded C programs, is proposed. It transforms a multi-threaded program into a corresponding sequential one and then uses a fault-diagnosis method suitable for this type of program, in order to localize faults. The code transformation is implemented with rules and context switch information from counterexamples, which are typically generated by bounded model checkers. Experimental results show that the proposed method is effective, in such a way that sequential fault-localization methods can be extended to multi-threaded programs.Comment: extended version of paper published at SBESC'1

Magnetic phases evolution in the LaMn1-xFexO3+y system

We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to x=1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn-Teller distortion, thus favoring a ferromagnetic (FM) superexchange (SE) interaction between Mn^{3+}-O-Mn^{3+}. For x=0.0 the oxygen excess (y ~ 0.09) produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn^{4+} ions and 82% of the usual Mn^{3+} ions, with possible double exchange interaction between them. The Fe doping in this system is known to produce only stable Fe^{3+} ions. We find an evolution from a fairly strong FM phase with a Curie temperature T_{C} ~ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with T_{N} = 790 K, for x=1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease (increase) of the FM (AFM) phase, accompanied by a systematic transition broadening for 0.2 < x < 0.7. A model based on the expected exchange interaction among the various magnetic-ion types, accounts very well for the saturation-magnetization dependence on Fe doping.Comment: 27 pages, 9 figure

Sliding Blocks Revisited: A simulational Study

A computational study of sliding blocks on inclined surfaces is presented. Assuming that the friction coefficient $\mu$ is a function of position, the probability $P(\lambda)$ for the block to slide down over a length $\lambda$ is numerically calculated. Our results are consistent with recent experimental data suggesting a power-law distribution of events over a wide range of displacements when the chute angle is close to the critical one, and suggest that the variation of $\mu$ along the surface is responsible for this.Comment: 6 pages, 4 figures. submitted to Int. J. Mod. Phys. (Proc. Brazilian Wokshop on Simulational Physics

On Matrix Superpotential and Three-Component Normal Modes

We consider the supersymmetric quantum mechanics (SUSY QM) with three- component normal modes for the Bogomol'nyi-Prasad-Sommerfield (BPS) states. An explicit form of the SUSY QM matrix superpotential is presented and the corresponding three-component bosonic zero-mode eigenfunction is investigated.Comment: 17 pages, no figure. Paper accepted for publication in Journal of Physics A: Mathematical and Theoretica

Chemical Potential and the Nature of the Dark Energy: The case of phantom

The influence of a possible non zero chemical potential $\mu$ on the nature of dark energy is investigated by assuming that the dark energy is a relativistic perfect simple fluid obeying the equation of state (EoS), $p=\omega \rho$ ($\omega <0, constant$). The entropy condition, $S \geq 0$, implies that the possible values of $\omega$ are heavily dependent on the magnitude, as well as on the sign of the chemical potential. For $\mu >0$, the $\omega$-parameter must be greater than -1 (vacuum is forbidden) while for $\mu < 0$ not only the vacuum but even a phantomlike behavior ($\omega <-1$) is allowed. In any case, the ratio between the chemical potential and temperature remains constant, that is, $\mu/T=\mu_0/T_0$. Assuming that the dark energy constituents have either a bosonic or fermionic nature, the general form of the spectrum is also proposed. For bosons $\mu$ is always negative and the extended Wien's law allows only a dark component with $\omega < -1/2$ which includes vacuum and the phantomlike cases. The same happens in the fermionic branch for $\mu 0$ are permmited only if $-1 < \omega < -1/2$. The thermodynamics and statistical arguments constrain the EoS parameter to be $\omega < -1/2$, a result surprisingly close to the maximal value required to accelerate a FRW type universe dominated by matter and dark energy ($\omega \lesssim -10/21$).Comment: 7 pages, 5 figure

Verkkosivujen käytettävyys Case: LaureaSID:n prototyyppi

Tämän opinnäytetyön aiheena on verkkosivuston käytettävyys. Opinnäytetyön tavoitteena on parantaa LaureaSID:n käyttöliittymän laatua tutkimalla prototyypin käytettävyyttä. Prototyyppiin tehdään parannus- ja korjausehdotuksia käytettävyysarvion perusteella. Käytettävyyden arviointiin käytimme kahta eri menetelmää: käytettävyystestiä ja heuristista asiantuntija arviota. Näistä menetelmistä toteutimme ensin käytettävyystestin, johon osallistui neljä LaureaSID:n eri kohderyhmiin kuuluvaa henkilöä. Käytettävyystestissä testihenkilöt suorittivat paperiprototyypillä kahdeksan ennalta määritettyä tehtävää. Toisena arviointimenetelmänä toteutimme heuristisen asiantuntija-arvion, jonka suorittivat neljä käytettävyyden asiantuntijaa. Asiantuntijat käyttivät sivuston tutkimiseen Jakob Nielsenin 10 heuristisen muistisääntöön perustuvaa listaa, jonka pohjalta he arvioivat sivuston käytettävyyttä. Käytettävyyden arvioinneissa esille tulleet käytettävyysongelmat on luokiteltu vakavuustaulukkoihin. Tekemämme tutkimuksen perusteella voidaan sanoa, että käytettävyyttä on hyvä arvioida jo aikaisen vaiheen prototyypillä. Arviointia olisi hyvä jatkaa myös sivuston tuotantoprosessin myöhemmissä vaiheissa. Molemmat käyttämämme arviointimenetelmät olivat hyödyllisiä tutkimuksen kannalta, ja ne tukivat hyvin toisiaan. Arviointien tuloksena löytyi eri vakavuusasteiden ongelmia. Sivusto on vasta prototyyppivaiheessa, eikä se sisällä toiminnallisuutta. Tästä johtuen vakavuusluokittelu toimii lähinnä suuntaa-antavana. Yleisesti vakavuus arvioidaan ongelmien toistuvuuden ja vaikutuksen perusteella.Website usability Case: LaureaSID’s prototype The topic of this thesis is website usability. The purpose of the thesis is to improve the quality of LaureaSID’s user interface by examining the usability of a prototype. Based on the usability evaluation, proposals for improving the prototype were given. Two different methods were used for the usability evaluation: a usability test and a heuristic evaluation. At first, four LaureaSID users from different target groups did the usability test. The test users executed eight tasks on a paper prototype. The second evaluation method was the heuristic evaluation that was carried out by four usability specialists. In order to evaluate the website usability, the specialists used a heuristic list based on Jakob Nielsen’s 10 heuristic general principles. All the usability errors were written down and classified to a severity chart. Based on the research, it can be stated that it is already important to evaluate the usability of the prototype at an early phase. Moreover, it would also be good to continue with the evaluation process also at the later phases of the website production. Both of the methods that were used for the usability evaluation were useful and they supported each other well. Based on the evaluation, different problem severity levels were found. The website is at the moment at the prototype phase and it does not have any functionalities. For that reason, the problem severity levels can be used only as indicatively. In general the severity is evaluated based on the problem repetitiveness and effect