Problems related to the integration of fault tolerant aircraft electronic systems

Problems related to the design of the hardware for an integrated aircraft electronic system are considered. Taxonomies of concurrent systems are reviewed and a new taxonomy is proposed. An informal methodology intended to identify feasible regions of the taxonomic design space is described. Specific tools are recommended for use in the methodology. Based on the methodology, a preliminary strawman integrated fault tolerant aircraft electronic system is proposed. Next, problems related to the programming and control of inegrated aircraft electronic systems are discussed. Issues of system resource management, including the scheduling and allocation of real time periodic tasks in a multiprocessor environment, are treated in detail. The role of software design in integrated fault tolerant aircraft electronic systems is discussed. Conclusions and recommendations for further work are included

Investigating Advances in the Acquisition of Secure Systems Based on Open Architecture, Open Source Software, and Software Product Lines

Naval Postgraduate School Acquisition Research Progra

Software Licenses in Context: The Challenge of Heterogeneously-Licensed Systems

The prevailing approach to free/open source software and licenses has been that each system is developed, distributed, and used under the terms of a single license. But it is increasingly common for information systems and other software to be composed with components from a variety of sources, and with a diversity of licenses. This may result in possible license conflicts and organizational liability for failure to fulfill license obligations. Research and practice to date have not kept up with this sea-change in software licensing arising from free/open source software development. System consumers and users consequently rely on ad hoc heuristics (or costly legal advice) to determine which license rights and obligations are in effect, often with less than optimal results; consulting services are offered to identify unknowing unauthorized use of licensed software in information systems; and researchers have shown how the choice of a (single) specific license for a product affects project success and system adoption. Legal scholars have examined how pairs of software licenses conflict but only in simple contexts. We present an approach for understanding and modeling software licenses, as well as for analyzing conflicts among groups of licenses in realistic system contexts, and for guiding the acquisition, integration, or development of systems with free/open source components in such an environment. This work is based on an empirical analysis of representative software licenses and of heterogeneously-licensed systems. Our approach provides guidance for achieving a “best-of-breed” component strategy while obtaining desired license rights in exchange for acceptable obligations

The \u3ci\u3eCryptococcus neoformans\u3c/i\u3e Flc1 Homologue Controls Calcium Homeostasis and Confers Fungal Pathogenicity in the Infected Hosts

Cryptococcus neoformans, an opportunistic yeast pathogen, relies on a complex network of stress response pathways that allow for proliferation in the host. In Saccharomyces cerevisiae, stress responses are regulated by integral membrane proteins containing a transient receptor potential (TRP) domain, including the flavin carrier protein 1 (Flc1), which regulates calcium homeostasis and flavin transport. Here, we report that deletion of C. neoformans FLC1 results in cytosolic calcium elevation and increased nuclear content of calcineurin-dependent transcription factor Crz1, which is associated with an aberrant cell wall chitin overaccumulation observed in the flc1Δ mutant. Absence of Flc1 or inhibition of calcineurin with cyclosporine A prevents vacuolar fusion under conditions of combined osmotic and temperature stress, which is reversed in the flc1Δ mutant by the inhibition of TORC1 kinase with rapamycin. Flc1-deficient yeasts exhibit compromised vacuolar fusion under starvation conditions, including conditions that stimulate formation of carbohydrate capsule. Consequently, the flc1Δ mutant fails to proliferate under low nutrient conditions and displays a defect in capsule formation. Consistent with the previously uncharacterized role of Flc1 in vacuolar biogenesis, we find that Flc1 localizes to the vacuole. The flc1Δ mutant presents a survival defect in J774A.1 macrophage cell-line and profound virulence attenuation in both the Galleria mellonella and mouse pulmonary infection models, demonstrating that Flc1 is essential for pathogenicity. Thus, cryptococcal Flc1 functions in calcium homeostasis and links calcineurin and TOR signaling with vacuolar biogenesis to promote survival under conditions associated with vacuolar fusion required for this pathogen’s fitness and virulence

Experimental modulation of capsule size in Cryptococcus neoformans

Experimental modulation of capsule size is an important technique for the study of the virulence of the encapsulated pathogen Cryptococcus neoformans. In this paper, we summarize the techniques available for experimental modulation of capsule size in this yeast and describe improved methods to induce capsule size changes. The response of the yeast to the various stimuli is highly dependent on the cryptococcal strain. A high CO(2) atmosphere and a low iron concentration have been used classically to increase capsule size. Unfortunately, these stimuli are not reliable for inducing capsular enlargement in all strains. Recently we have identified new and simpler conditions for inducing capsule enlargement that consistently elicited this effect. Specifically, we noted that mammalian serum or diluted Sabouraud broth in MOPS buffer pH 7.3 efficiently induced capsule growth. Media that slowed the growth rate of the yeast correlated with an increase in capsule size. Finally, we summarize the most commonly used media that induce capsule growth in C. neoformans

Defects in intracellular trafficking of fungal cell wall synthases lead to aberrant host immune recognition

Acknowledgments We acknowledge Jeanette Wagener and Louise Walker for performing the HPAEC-PAD analysis and Neil Gow for providing access to the Dionex HPAEC-PAD instrumentation. We thank Mike Cook and the Duke University Cancer Center Flow Cytometry Shared Resource for assistance with the flow cytometry. We also acknowledge Michelle Plue and the Duke University Shared Materials Institute Facility for performing the transmission electron microscopy. We thank Marcel Wu¨thrich for providing the MyD88-/-and TLR2/4-/- mice, and Mari Shinohara and Elizabeth Deerhake for providing the Dectin-1-/- mice. Funding: These experiments were supported by a National Institutes of Health grant awarded to JAA and FLW, Jr. (R01 AI074677, https://grants.nih.gov/grants/oer.html). CM and colleagues Jeanette Wagener, Louise Walker, Neil Gow were supported by the Wellcome Trust Strategic Award in Medical Mycology and Fungal Immunology (097377, https://wellcome.ac.uk), Wellcome Trust Senior Investigator Award (101873) and the MRC Centre for Medical Mycology (MR/N006364/1, https://www.abdn.ac.uk/cmm/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Remasking of Candida albicans β-Glucan in Response to Environmental pH Is Regulated by Quorum Sensing

Candida albicans is a commensal yeast of the human gut which is tolerated by the immune system but has the potential to become an opportunistic pathogen. One way in which C. albicans achieves this duality is through concealing or exposing cell wall pathogen-associated molecular patterns (PAMPs) in response to host-derived environment cues (pH, hypoxia, and lactate). This cell wall remodeling allows C. albicans to evade or hyperactivate the host’s innate immune responses, leading to disease. Previously, we showed that adaptation of C. albicans to acidic environments, conditions encountered during colonization of the female reproductive tract, induces significant cell wall remodeling resulting in the exposure of two key fungal PAMPs (β-glucan and chitin). Here, we report that this pH-dependent cell wall remodeling is time dependent, with the initial change in pH driving cell wall unmasking, which is then remasked at later time points. Remasking of β-glucan was mediated via the cell density-dependent fungal quorum sensing molecule farnesol, while chitin remasking was mediated via a small, heat-stable, nonproteinaceous secreted molecule(s). Transcript profiling identified a core set of 42 genes significantly regulated by pH over time and identified the transcription factor Efg1 as a regulator of chitin exposure through regulation of CHT2. This dynamic cell wall remodeling influenced innate immune recognition of C. albicans, suggesting that during infection, C. albicans can manipulate the host innate immune responses

The Cryptococcus neoformans Rim101 Transcription Factor Directly Regulates Genes Required for Adaptation to the Host

The Rim101 protein is a conserved pH-responsive transcription factor that mediates important interactions between several fungal pathogens and the infected host. In the human fungal pathogen Cryptococcus neoformans, the Rim101 protein retains conserved functions to allow the microorganism to respond to changes in pH and other host stresses. This coordinated cellular response enables this fungus to effectively evade the host immune response. Preliminary studies suggest that this conserved transcription factor is uniquely regulated in C. neoformans both by the canonical pH-sensing pathway and by the cyclic AMP (cAMP)/protein kinase A (PKA) pathway. Here we present comparative transcriptional data that demonstrate a strong concordance between the downstream effectors of PKA and Rim101. To define Rim101-dependent gene expression during a murine lung infection, we used nanoString profiling of lung tissue infected with a wild-type or rim101Δ mutant strain. In this setting, we demonstrated that Rim101 controls the expression of multiple cell wall-biosynthetic genes, likely explaining the enhanced immunogenicity of the rim101Δ mutant. Despite its divergent upstream regulation, the C. neoformans Rim101 protein recognizes a conserved DNA binding motif. Using these data, we identified direct targets of this transcription factor, including genes involved in cell wall regulation. Therefore, the Rim101 protein directly controls cell wall changes required for the adaptation of C. neoformans to its host environment. Moreover, we propose that integration of the cAMP/PKA and pH-sensing pathways allows C. neoformans to respond to a broad range of host-specific signals