Algorithms for four variants of the exact satisfiability problem

We present four polynomial space and exponential time algorithms for variants of the E S problem. First, an O(1.1120ⁿ) (where n is the number of variables) time algorithm for the NP-complete decision problem of E 3-S , and then an O(1.1907ⁿ) time algorithm for the general decision problem of E S . The best previous algorithms run in O(1.1193ⁿ) and O(1.2299ⁿ) time, respectively. For the #P-complete problem of counting the number of models for E 3-S we present an O(1.1487ⁿ) time algorithm. We also present an O(1.2190ⁿ) time algorithm for the general problem of counting the number of models for E S ; presenting a simple reduction, we show how this algorithm can be used for computing the permanent of a 0/1 matrix.     

Application of autocorrelation analysis for interpreting acoustic emission in rock

The statistical properties of acoustic emission from rock samples were studied as a function of applied uniaxial load. It was found that the parameters of the autocorrelation function of the acoustic emission event series change significantly near failure. An increase in the values of the autocorrelation coefficients and a tendency to a linear decrease with time were observed. We propose that the increasing autocorrelation of the acoustic emission series is an evidence of the increased affect that the individual acoustic emission sources have on one another. This mutual effect of acoustic events arises as a result of the redistribution of stress in the sample during the fracturing process at higher loads (more than 95% of ultimate strength). The results support the possibility of using autocorrelation analysis as a failure warning sign or even to predict the sample's total failure. Different rock materials and various loading patterns were used to generalise the results obtained.     

Phototoxicity of pyrene affects benthic algae and bacteria from the Arctic

Phototoxicity of polycyclic aromatic hydrocarbons (PAHs) in the Arctic is important to study since the future PAH load is likely to increase. In combination with the increased UV-light penetration due to ozone layer thinning, phototoxicity may be a potential problem for arctic areas. The aim of this study was to evaluate effects of pyrene and phototoxicity of pyrene on natural algae and bacteria from arctic sediments. Sediments from a shallow-water marine baywere spiked with different pyrene concentrations. Microcosms containing the sediment were incubated under three light regimes, natural sunlight with UV-light, natural sunlight without UV-light, and dark. Significant effects were evident at low pyrene concentrations, particularly in presence of UV-light, indicating phototoxicity. The microalgae were especially sensitive to the phototoxicity of pyrene. Already atthe lowest pyrene concentration (Cfree: 4 nM) algal 14C-incorporation and chlorophyll a content were reduced. The toxic effects of pyrene on the microalgae probably led to the release of organic matter. In agreement with this, bacterial activity increased at high pyrene concentrations indicated by increased oxygen consumption and increased release of inorganic N and P from the sediment. This study indicates that phototoxicity of PAHs may be relevant for sediment communities from shallow marine arctic areas at environmentally relevant pyrene concentrations.     

Effects of navigation method on workload and performance in simulated high-speed ship navigation

This study examines mental workload and performance in simulated high-speed ship navigation. Two navigation methods were compared based on an electronic chart display and information system (ECDIS) and a conventional system using paper charts. Twenty naval cadets navigated in high-fidelity simulators through a 50 nautical mile course with varying levels of difficulty. Results showed that ECDIS navigation significantly improved course-keeping performance, but reduced the total amount of communication on the bridge. No differences were observed in subjective workload between groups. Heart rate variability and skin conductance measurements indicated higher workload in conventional navigation, but the differences between groups were not significant.     

Combining disparate sources of information in the safety assessment of software-based systems

The main topic of the paper is a discussion on how to combine disparate sources of information in the safety assessment of software-based systems. This is based on experience gained through the licensing process of a programmable system in the Swedish nuclear power plant Ringhals, where a guideline for reviewing software in safety-related systems was applied. One lesson learned from this activity is that the approval of a programmable safety critical system, in particular one which is based on Commercial-Off-The-Shelf software, is based on a combination of disparate sources of information. This combination of information is made in a diagrammatic framework. An emerging methodology to combine information about disparate evidences in a systematic way is based on Bayesian Belief Networks. The objective is to show the link between basic information and the confidence one can have in a system.     

Dental maturity in children of short stature, with or without growth hormone deficiency

Macrophages are important constituents of the immune system by exerting phagocytosis on invading pathogens as well as secreting various immunoregulatory factors. Generation of human macrophage hybridoma has not been possible so far due to the lack of an appropriate fusion partner cell line. In the present study, an 8'-azaguanine resistant cell line, termed HL-60R, was established by drug selection of the promyelocytic cell line HL-60. This novel cell line showed resistance to high concentrations of 8'-azaguanine and was sensitive to aminopterin. These characteristics make it suitable for serving as a potential fusion partner cell line in the development of macrophage hybridoma. Cell-surface analysis by FACS revealed that HL-60R cells per se do not express MHC-class II molecules or the macrophage marker, CD11b. PEG-mediated fusion of HL-60R was performed with PBMC-derived human macrophages. Fluorescence labelling of ex vivo isolated macrophages prior to fusion and subsequent FACS analysis showed that PEG-4000 is a more effective fusion agent than PEG-1500. The generation of this novel fusion partner cell line opens the possibility for development of human macrophage hybridoma or other cell lines from myelocytic origin. Such hybridoma clones will not only enable a more convenient study of these cell but will also provide an excellent host site for the proper production and expression of various recombinant proteins from myelocytic origin in vitro.     

Software diversity: Way to enhance safety?

The topic of the paper is the use of diversely produced programs to enhance the safety of computer-based systems applied in safety-critical areas. The paper starts with a survey of scientific investigations on the impact of software redundancy made at various institutions around the world. Main emphasis will, however, be put on the PODS/STEM projects, which have been performed at the OECD Halden Project in cooperation with the Technical Research Center of Finland, the Safety and Reliability Directorate, AEA Technology, UK, and Central Electricity Research Laboratory (now National Power Technology and Environment Centre), UK. In these projects, three program versions were made independently by three different teams, all based on the same specification. The three programs were tested back-to-back with a large amount of test data. The experience and results from this process were carefully logged and used for further analysis. Various strategies for test data selection were compared, with respect to fault finding strategies, as well as to branch and statement coverages of the tested programs. The assumption of independence of failures in diversely produced programs was investigated. A particularly interesting effect, namely, failure masking due to program structure, was revealed. Static analysis techniques, software measures, and software reliability estimates were also studied.     

Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot

In this work, a mini-CAST soot generator was used to produce soot with different optical and physicochemical characteristics. Absorption Ångström exponents (AAE) expressing the absorption wavelength dependence were assessed by multiwavelength in-situ and filter-based (aethalometer) laser extinction. The two optical techniques showed good agreement. For the chosen mini-CAST operating conditions, AAEs between 1 and 3.5 were found. Soot with high mass-fractions of organic carbon (OC) and pyrolytic carbon (PC) determined with thermal optical analysis were associated with AAEs significantly higher than 1. Heating to 250 and 500°C removed the majority of polycyclic aromatic hydrocarbons. However, the thermal-optical analysis revealed that OC and PC were abundant in the soot with AAE > 2 also after heating the aerosol. Analysis of mass absorption cross section ratios for elemental carbon and OC indicated that elevated AAEs also after heating to 500°C could be related to persistent OC and PC components and/or the refractory soot. By comparing the mini-CAST soot optical properties with soot properties derived from in-situ extinction measurements in a premixed flame, mini-CAST soot with a higher AAE could be identified as less mature soot.

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