System fault-tolerance analysis of COTS-based satellite on-board computers

Fault-tolerance analysis reveals possible system behavior under the influence of faults. Such analysis is essential for satellites where faults might be caused by space radiation and autonomous recovery is needed. In this paper we present a statistical simulation approach for fault-tolerance analysis of satellite On-Board Computers (OBCs) that are based on Commercial Off-The-Shelf (COTS) components. Since the logic level of COTS electronics is unknown to satellite designers, a new higher-level fault-tolerance analysis is required. We propose such technique that relies on OBC modeling and fault modeling, based on the modeling principle of Single-Event Upsets (SEUs). For the first time we can compare the efficiency of fault-tolerance techniques implemented in software and Field-Programmable Gate Array (FPGA). In addition, our approach enables to analyze system fault-tolerance at early development stages. In a case study the approach is applied to an OBC with a Microsemi SmartFusion SoC, that executes a satellite attitude control algorithm. The gained statistical simulation results enabled 50% reduction in the hardware overhead of the implemented memory scrubbing technique without loss in fault-tolerance. Our method revealed critical fault-tolerance drawbacks of the initial system design that could have lead to satellite mission failure.     

Phytochelatin synthase activity as a marker of metal pollution

The synthesis of phytochelatins is catalyzed by γ-Glu-Cys dipeptidyl transpeptidase called phytochelatin synthase (PCS). Aim of this study was to suggest a new tool for determination of phytochelatin synthase activity in the tobacco BY-2 cells treated with different concentrations of the Cd(II). After the optimization steps, an experiment on BY-2 cells exposed to different concentrations of Cd(NO₃)₂ for 3 days was performed. At the end of the experiment, cells were harvested and homogenized. Reduced glutathione and cadmium (II) ions were added to the cell suspension supernatant. These mixtures were incubated at 35 °C for 30 min and analysed using high performance liquid chromatography coupled with electrochemical detector (HPLC-ED). The results revealed that PCS activity rises markedly with increasing concentration of cadmium (II) ions. The lowest concentration of the toxic metal ions caused almost three fold increase in PCS activity as compared to control samples. The activity of PCS (270 fkat) in treated cells was more than seven times higher in comparison to control ones. K_m for PCS was estimated as 2.3 mM.     

Aligned nanowires and nanodots by directed block copolymer assembly

The directed self-assembly of block copolymers (BCPs) is a promising route to generate highly ordered arrays of sub-10 nm features. Ultradense arrays of a monolayer of spherical microdomains or cylindrical microdomains oriented parallel to the surface have been produced where the lateral ordering is guided by surface patterning and the lattice defined by the patterning can be commensurate or incommensurate with the natural period of the BCP. Commensurability between the two can be used to elegantly manipulate the lateral ordering and orientation of the BCP microdomains so as to form well-aligned arrays of 1D nanowires or 2D addressable nanodots. No modification of the substrate surface, aside from the patterning, was used, making the influence of lattice mismatch and pattern amplification on the size, shape and pitch of the BCP microdomains more transparent. A skew angle between incommensurate lattices, defining a stretching or compression of the BCP chains to compensate for the lattice mismatch, is presented.     

The effects of password length and reference profile size on the performance of a multivariate text-dependent typist verification system

The performance of Napier et al.'s typist verification algorithm (Keyboard user verification: toward an accurate, efficient, and ecologically valid algorithm, International Journal of Human-Computer Studies 43 (1995) 213-222) was assessed in a text-dependent setting. Twenty-nine subjects typed a 17 character password 50 times. False acceptance and false rejection rates were then calculated as the number of repetitions of the password included in the reference profile was increased from 6 to 20 and the number of digraphs from the password included in the verification process was increased from 2 to 16. The performance of the system (12% total error rate) was found to be comparable with the best results reported in other studies using text-dependent algorithms, and substantially better than that reported in studies using a text-independent paradigm with passwords of this length. The relationship between password length and reference profile size was found to conform to an exponential decay function, which accounted for 92% of the variability in verification error rates.     

An overview of the development of the first wall and other principal components of a laser fusion power plant

This paper introduces the JNM Special Issue on the development of a first wall for the reaction chamber in a laser fusion power plant. In this approach to fusion energy a spherical target is injected into a large chamber and heated to fusion burn by an array of lasers. The target emissions are absorbed by the wall and encapsulating blanket, and the resulting heat converted into electricity. The bulk of the energy deposited in the first wall is in the form of X-rays (1.0-100 keV) and ions (0.1-4 MeV). In order to have a practical power plant, the first wall must be resistant to these emissions and suffer virtually no erosion on each shot. A wall candidate based on tungsten armor bonded to a low activation ferritic steel substrate has been chosen as the initial system to be studied. The choice was based on the vast experience with these materials in a nuclear environment and the ability to address most of the key remaining issues with existing facilities. This overview paper is divided into three parts. The first part summarizes the current state of the development of laser fusion energy. The second part introduces the tungsten armored ferritic steel concept, the three critical development issues (thermo-mechanical fatigue, helium retention, and bonding) and the research to address them. Based on progress to date the latter two appear to be resolvable, but the former remains a challenge. Complete details are presented in the companion papers in this JNM Special Issue. The third part discusses other factors that must be considered in the design of the first wall, including compatibility with blanket concepts, radiological concerns, and structural considerations.     

Fumonisin production and other traits of Fusarium moniliforme strains from maize in northeast Mexico

Strains of Fusarium moniliforme from maize seed collected in four fields in northeast Mexico were tested for fumonisin production in culture, for sexual compatibility, and for vegetative compatibility by using non-nitrate-utilizing mutants. The test results indicate that a diverse population of fumonisin-producing strains of F. moniliforme (Gibberella fujikuroi) mating population A predominates and that a potential exists for production of fumonisins in Mexican maize.     

Survival strategies of Leishmania donovani in mammalian host macrophages

Microbes have evolved a variety of strategies to survive inside their host cells. Some have the molecular machinery to survive in the hostile environment of phagolysosomes; others escape the phagosome to the more cozy environment of the cell cytoplasm; others inhibit the phagosome fusion with hydrolase-enriched endocytic organelles. This is the case for the promastigote form of the protozoan parasite Leishmania donovani which resides in a phagosome displaying poor fusogenic properties towards endosomes and lysosomes. Recent results indicate that the lipophosphoglycan (LPG), the major cell surface molecule of Leishmania, is involved in the inhibition of phagosome maturation. Further studies in our laboratories are addressing the molecular mechanisms of action of LPG to modulate phagosome fusion properties and its effect on the biogenesis of phagolysosomes.     

Slow twin conception at first birth and subsequent maternal twin proneness in a natural fertility population

To study whether apparently more fecund women having delivered twins at first birth have traits of higher twin-proneness, we performed a retrospective cohort study on population-based historical vital records of the 17-18th century French Canadian immigrants and their descendants under natural fertility conditions. Among 24896 mothers who had at least one child, 248 had twin maternities at their first birth (twinning rate = 1.0%). Among 21508 mothers with a valid marriage-first birth interval, twinning rate was 0.97% among prompt conceptions (7.0-11.0 months), with a particularly high rate at the interval of 7.0-8.0 months (2.2%). Marriages in August-October resulted in a higher twinning rate particularly for the slow conceptions than those in the other seasons. Promptly-conceived mothers of twins at the first delivery may seem to have higher fecundity, but subsequent births from these mothers (n = 88) show a lower twinning rate (1.7%) particularly at younger maternal age than from the other mothers who had slowly conceived twins at their first birth (n = 112). The latter show a 4.5% twinning rate as a whole among their second or later births. So-called twin-proneness of a mother, whether genetic or acquired, was not connected to higher conception rate of twin's mothers immediately after marriage. Reduced fecundity, which may have been imposed by some environmental factors, could raise the chance of twinning.