Towards the Automated Verification of Weibull Distributions for System Failure Rates

Weibull distributions can be used to accurately model failure behaviours of a wide range of critical systems such as on-orbit satellite subsystems. Markov chains have been used extensively to model reliability and performance of engineering systems or applications. However, the exponentially distributed sojourn time of Continuous-Time Markov Chains (CTMCs) can sometimes be unrealistic for satellite systems that exhibit Weibull failures. In this paper, we develop novel semi-Markov models that characterise failure behaviours, based on Weibull failure modes inferred from realistic data sources. We approximate and encode these new models with CTMCs and use the PRISM probabilistic model checker. The key bene t of this integration is that CTMC-based model checking tools allow us to automatically and e ciently verify reliability properties relevant to industrial critical systems

Antiferromagnetic Phases of One-Dimensional Quarter-Filled Organic Conductors

The magnetic structure of antiferromagnetically ordered phases of quasi-one-dimensional organic conductors is studied theoretically at absolute zero based on the mean field approximation to the quarter-filled band with on-site and nearest-neighbor Coulomb interaction. The differences in magnetic properties between the antiferromagnetic phase of (TMTTF)$_2$X and the spin density wave phase in (TMTSF)$_2$X are seen to be due to a varying degrees of roles played by the on-site Coulomb interaction. The nearest-neighbor Coulomb interaction introduces charge disproportionation, which has the same spatial periodicity as the Wigner crystal, accompanied by a modified antiferromagnetic phase. This is in accordance with the results of experiments on (TMTTF)$_2$Br and (TMTTF)$_2$SCN. Moreover, the antiferromagnetic phase of (DI-DCNQI)$_2$Ag is predicted to have a similar antiferromagnetic spin structure.Comment: 8 pages, LaTeX, 4 figures, uses jpsj.sty, to be published in J. Phys. Soc. Jpn. 66 No. 5 (1997

Optical properties of perovskite alkaline earth titanates : a formulation

In this communication we suggest a formulation of the optical conductivity as a convolution of an energy resolved joint density of states and an energy-frequency labelled transition rate. Our final aim is to develop a scheme based on the augmented space recursion for random systems. In order to gain confidence in our formulation, we apply the formulation to three alkaline earth titanates CaTiO_3, SrTiO_3 and BaTiO_3 and compare our results with available data on optical properties of these systems.Comment: 19 pages, 9 figures, Submitted to Journal of Physics: Condensed Matte

Superconductivity and Density Wave in the Quasi-One-Dimensional Systems: Renormalization Group Study

The anisotropic superconductivity and the density wave have been investigated by applying the Kadanoff-Wilson renormalization group technique to the quasi-one-dimensional system with finite-range interactions. It is found that a temperature (T) dependence of response functions is proportional to exp(1/T) in a wide region of temperature even within the one-loop approximation. Transition temperatures are calculated to obtain the phase diagram of the quasi-one-dimensional system, which is compared with that of the pure-one-dimensional system. Next-nearest neighbor interactions (V_2) induce large charge fluctuations, which suppress the d_{x^2 -y^2}-wave singlet superconducting (dSS) state and enhance the f-wave triplet superconducting (fTS) state. From this effect, the transition temperature of fTS becomes comparable to that of dSS for large V_2, so that field-induced f-wave triplet pairing could be possible. These features are discussed to comprehend the experiments on the (TMTSF)_2PF_6 salt.Comment: 8 pages, 4 figures, submitted to J. Phys. Soc. Jp

Exploring the Energy Landscape of the Charge Transport Levels in Organic Semiconductors at the Molecular Scale

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Evaluation of the impact of pharmaceutical trainings and tools on the proper use of medicines in pediatrics

Introduction: After six years of medication errors’ (MEs) collection and analysis in a pediatric unit of a French University Hospital, the number of MEs was no longer decreasing. We then decided to set up pharmaceutical training and tools and evaluate their impact on the occurrence of ME.Materials and methods: This monocentric prospective study was carried out in the form of audits of prescriptions, preparations, and administrations before and after intervention (A1 and A2). After the analysis of A1 results, feedback was given to the teams, some tools for the proper use of medication (PUM) were distributed, and A2 was conducted. Finally, A1 and A2 results were compared.Results: Each audit included 202 observations. A total of 120 MEs were identified during A1 and 54 for A2 (p < 0.0001). The observation rate with at least 1 ME decreased from 39.11% to 21.29% (p < 0.0001), and no observation had more than two MEs during A2 in contrast to A1 (n = 12). Human factors were responsible for the majority of MEs. The audit feedback allowed professionals to feel concerned about ME. The PUM tools received an average satisfaction rating of 9/10. The staff had never participated in this type of training, and all felt it was useful to apply PUM.Conclusion: This study showed a significant impact of pharmaceutical training and tools on the pediatric PUM. Clinical pharmaceutic actions allowed us to reach our objectives and satisfied all the staff. They must, therefore, be continued to limit human factors’ impact and thus contribute to the safety of drug management in pediatrics

Effect of nearest- and next-nearest neighbor interactions on the spin-wave velocity of one-dimensional quarter-filled spin-density-wave conductors

We study spin fluctuations in quarter-filled one-dimensional spin-density-wave systems in presence of short-range Coulomb interactions. By applying a path integral method, the spin-wave velocity is calculated as a function of on-site (U), nearest (V) and next-nearest (V_2) neighbor-site interactions. With increasing V or V_2, the pure spin-density-wave state evolves into a state with coexisting spin- and charge-density waves. The spin-wave velocity is reduced when several density waves coexist in the ground state, and may even vanish at large V. The effect of dimerization along the chain is also considered.Comment: REVTeX, 11 pages, 9 figure

Dielectric response of charge induced correlated state in the quasi-one-dimensional conductor (TMTTF)2PF6

Conductivity and permittivity of the quasi-one-dimensionsional organic transfer salt (TMTTF)2PF6 have been measured at low frequencies (10^3-10^7 Hz) between room temperature down to below the temperature of transition into the spin-Peierls state. We interpret the huge real part of the dielectric permittivity (up to 10^6) in the localized state as the realization in this compound of a charge ordered state of Wigner crystal type due to long range Coulomb interaction.Comment: 11 pages, 3 .eps figure

Large-N solutions of the Heisenberg and Hubbard-Heisenberg models on the anisotropic triangular lattice: application to Cs2_2CuCl4_4 and to the layered organic superconductors κ\kappa-(BEDT-TTF)2_2X

We solve the Sp(N) Heisenberg and SU(N) Hubbard-Heisenberg models on the anisotropic triangular lattice in the large-N limit. These two models may describe respectively the magnetic and electronic properties of the family of layered organic materials $\kappa$-(BEDT-TTF)$_2$X. The Heisenberg model is also relevant to the frustrated antiferromagnet, Cs$_2$CuCl$_4$. We find rich phase diagrams for each model. The Sp(N) antiferromagnet is shown to have five different phases as a function of the size of the spin and the degree of anisotropy of the triangular lattice. The effects of fluctuations at finite-N are also discussed. For parameters relevant to Cs$_2$CuCl$_4$ the ground state either exhibits incommensurate spin order, or is in a quantum disordered phase with deconfined spin-1/2 excitations and topological order. The SU(N) Hubbard-Heisenberg model exhibits an insulating dimer phase, an insulating box phase, a semi-metallic staggered flux phase (SFP), and a metallic uniform phase. The uniform and SFP phases exhibit a pseudogap. A metal-insulator transition occurs at intermediate values of the interaction strength.Comment: Typos corrected, one reference added. 20 pages, 17 figures, RevTeX 3.

Charge Ordering in Organic ET Compounds

The charge ordering phenomena in quasi two-dimensional 1/4-filled organic compounds (ET)_2X (ET=BEDT-TTF) are investigated theoretically for the $\theta$ and $\alpha$-type structures, based on the Hartree approximation for the extended Hubbard models with both on-site and intersite Coulomb interactions. It is found that charge ordered states of stripe-type are stabilized for the relevant values of Coulomb energies, while the spatial pattern of the stripes sensitively depends on the anisotropy of the models. By comparing the results of calculations with the experimental facts, where the effects of quantum fluctuation is incorporated by mapping the stripe-type charge ordered states to the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating phases of $\theta$-(ET)_2MM'(SCN)_4 and $\alpha$-(ET)_2I_3 are deduced. Furthermore, to obtain a unified view among the $\theta$, $\alpha$ and $\kappa$-(ET)_2X families, the stability of the charge ordered state in competition with the dimeric antiferromagnetic state viewed as the Mott insulating state, which is typically realized in $\kappa$-type compounds, and with the paramagnetic metallic state, is also pursued by extracting essential parameters.Comment: 35 pages, 27 figures, submitted to J. Phys. Soc. Jp