Choosing effective methods for design diversity - How to progress from intuition to science

Design diversity is a popular defence against design faults in safety critical systems. Design diversity is at times pursued by simply isolating the development teams of the different versions, but it is presumably better to "force" diversity, by appropriate prescriptions to the teams. There are many ways of forcing diversity. Yet, managers who have to choose a cost-effective combination of these have little guidance except their own intuition. We argue the need for more scientifically based recommendations, and outline the problems with producing them. We focus on what we think is the standard basis for most recommendations: the belief that, in order to produce failure diversity among versions, project decisions should aim at causing "diversity" among the faults in the versions. We attempt to clarify what these beliefs mean, in which cases they may be justified and how they can be checked or disproved experimentally

On Systematic Design of Protectors for Employing OTS Items

Off-the-shelf (OTS) components are increasingly used in application areas with stringent dependability requirements. Component wrapping is a well known structuring technique used in many areas. We propose a general approach to developing protective wrappers that assist in integrating OTS items with a focus on the overall system dependability. The wrappers are viewed as redundant software used to detect errors or suspicious activity and to execute appropriate recovery when possible; wrapper development is considered as a part of system integration activities. Wrappers are to be rigorously specified and executed at run time as a means of protecting OTS items against faults in the rest of the system, and the system against the OTS item's faults. Possible symptoms of erroneous behaviour to be detected by a protective wrapper and possible actions to be undertaken in response are listed and discussed. The information required for wrapper development is provided by traceability analysis. Possible approaches to implementing “protectors” in the standard current component technologies are briefly outline

Medical card of a pulmonary tuberculosis in-patient

ИСТОРИЯ БОЛЕЗНИОБСЛЕДОВАНИЕ БОЛЬНОГОТУБЕРКУЛЕЗ ЛЕГКИХУЧЕБНО-МЕТОДИЧЕСКИЕ ПОСОБИЯФТИЗИОПУЛЬМОНОЛОГИЯУчебно-методическое пособие предназначено для самостоятельной подготовки к курации больных в клинике и написанию учебной истории болезни

From Analysing Operating System Vulnerabilities to Designing Multiversion Intrusion-Tolerant Architectures

This paper analyses security problems of modern computer systems caused by vulnerabilities in their operating systems. Our scrutiny of widely used enterprise operating systems focuses on their vulnerabilities by examining the statistical data available on how vulnerabilities in these systems are disclosed and eliminated, and by assessing their criticality. This is done by using statistics from both the National Vulnerabilities database (NVD) and the Common Vulnerabilities and Exposures system (CVE). The specific technical areas the paper covers are the quantitative assessment of forever-day vulnerabilities, estimation of days-of-grey-risk, the analysis of the vulnerabilities severity and their distributions by attack vector and impact on security properties. In addition, the study aims to explore those vulnerabilities that have been found across a diverse range of operating systems. This leads us to analysing how different intrusion-tolerant architectures deploying the operating system diversity impact availability, integrity and confidentiality

Software Development in the Post-PC Era: Towards Software Development as a Service

Abstract. Software systems affect all aspects of our modern life andare revolutionizing the way we live. Over the years, software developmenthas evolved to meet the needs of new types of applications and toembrace new technological disruptions. Today, we witness the rise of mobilitywhere the role of the conventional high-specification PC is declining.Some refer to this era as the Post-PC era. This technological shift,powered by a key enabling technology - cloud computing, has opened new opportunities for human advancement (e.g. the Internet of Things).Consequently, the evolving landscape of software systems drives the need for new methods for conceiving them. Such methods need to a) address the challenges and requirements of this era and b) embrace the benefitsof new technological breakthroughs. In this paper, we list the characteristics of the Post-PC era from the software development perspective. In addition, we describe three motivating trends of software development processes. Then, we derive a list of requirements for the future software development approach from the characteristics of the Post-PC era and from the motivating trends. Finally, we propose a reference architecturefor cloud-based software process enactment as an enabler for Software Development as a Service (SDaaS). The architecture is thefirst step to address the needs that we have identified

Edge states in graphene quantum dots: Fractional quantum Hall effect analogies and differences at zero magnetic field

We investigate the way that the degenerate manifold of midgap edge states in quasicircular graphene quantum dots with zig-zag boundaries supports, under free-magnetic-field conditions, strongly correlated many-body behavior analogous to the fractional quantum Hall effect (FQHE), familiar from the case of semiconductor heterostructures in high magnetic fields. Systematic exact-diagonalization (EXD) numerical studies are presented for the first time for 5 <= N <= 8 fully spin-polarized electrons and for total angular momenta in the range of N(N-1)/2 <= L <= 150. We present a derivation of a rotating-electron-molecule (REM) type wave function based on the methodology introduced earlier [C. Yannouleas and U. Landman, Phys. Rev. B 66, 115315 (2002)] in the context of the FQHE in two-dimensional semiconductor quantum dots. The EXD wave functions are compared with FQHE trial functions of the Laughlin and the derived REM types. It is found that a variational extension of the REM offers a better description for all fractional fillings compared with that of the Laughlin functions (including total energies and overlaps), a fact that reflects the strong azimuthal localization of the edge electrons. In contrast with the multiring arrangements of electrons in circular semiconductor quantum dots, the graphene REMs exhibit in all instances a single (0,N) polygonal-ring molecular (crystalline) structure, with all the electrons localized on the edge. Disruptions in the zig-zag boundary condition along the circular edge act effectively as impurities that pin the electron molecule, yielding single-particle densities with broken rotational symmetry that portray directly the azimuthal localization of the edge electrons.Comment: Revtex. 14 pages with 13 figures and 2 tables. Physical Review B, in press. For related papers, see http://www.prism.gatech.edu/~ph274cy