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  • Random walks  (6)
  • COMPUTER PROGRAMMING AND SOFTWARE  (4)
  • 2000-2004
  • 1985-1989  (10)
  • 1960-1964
  • 1945-1949
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 44 (1986), S. 933-939 
    ISSN: 1572-9613
    Schlagwort(e): Random walks ; trapping ; reaction rates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This note contains a formalism for calculating properties of random walks in the presence of a set of partially absorbing traps. The properties that are considered are the probability of trapping at a specific point and the survival probability as a function of step number. The results are expressed in terms of determinants, but approximations to these can be found.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 57 (1989), S. 301-317 
    ISSN: 1572-9613
    Schlagwort(e): Random walks ; disordered media ; transport properties
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We derive asymptotic properties of the propagatorp(r,t) of a continuous-time random walk (CTRW) in which the waiting time density has the asymptotic formψ(t)∼T α/t α+1 whent≫T and 0〈α〈1. Several cases are considered; the main ones are those that assume that the variance of the displacement in a single step of the walk is finite. Under this assumption we consider both random walks with and without a bias. The principal results of our analysis is that one needs two forms to characterizep(r,t), depending on whetherr is large or small, and that the small-r expansion cannot be characterized by a scaling form, although it is possible to find such a form for larger. Several results can be demonstrated that contrast with the case in which 〈t〉=∫ 0 ∞ τψ(τ)dτ is finite. One is that the asymptotic behavior ofp(0,t) is dominated by the waiting time at the origin rather than by the dimension. The second difference is that in the presence of a fieldp(r,t) no longer remains symmetric around a moving peak. Rather, it is shown that the peak of this probability always occurs atr=0, and the effect of the field is to break the symmetry that occurs when 〈t〉∞. Finally, we calculate similar properties, although in not such great detail, for the case in which the single-step jump probabilities themselves have an infinite mean.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 40 (1985), S. 191-199 
    ISSN: 1572-9613
    Schlagwort(e): Random walks ; trapping ; Tauberian theorems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We consider the survival of a random walker in a finite lattice with periodic boundary conditions. The initial position of the random walker is uniformly distributed on the lattice with respect to the trap. We show that the survival of a random walker, 〈U n〉, can be exactly related to the expected number of distinct sites visted on a trap-free lattice by 〈U n〉=1−〈S n〉/N D (*) whereN D is the number of lattice points inD dimensions. We then analyze the behavior of 〈Sn〉 in any number of dimensions by using Tauberian methods. We find that at sufficiently long times 〈S n〉 decays exponentially withn in all numbers of dimensions. InD = 1 and 2 dimensions there is an intermediate behavior which can be calculated and is valid forN 2≫N ≫ 1 whenD = 1 andN lnN ≫n≫ 1 whenD = 2. No such crossover exists when Z⩾3. The form of (*) suggests that the single trap approximation is indeed a valid low-concentration limit for survival on an infinite lattice with a finite concentration of traps.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 47 (1987), S. 173-184 
    ISSN: 1572-9613
    Schlagwort(e): Random walks ; random media ; scaling behavior
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present analytical and numerical results for the probability distributions of the number of sitesS as a function of the number of shellsl for several ensembles of percolation clusters generated on a Cayley tree at criticality. We find that for the incipient infinite percolation cluster the probability distribution isP(S¦l)~(S/l 4)exp(- aS/l 2) for S≫l≫1.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 52 (1988), S. 287-293 
    ISSN: 1572-9613
    Schlagwort(e): Random walks ; stable laws ; measures of asymmetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We derive the probability density for a simple measure of the asymmetry of a one-dimensional random walk, namely the ratio of the minimum of the two maximum displacements in the positive and negative directions, to the maximum. We show that in the diffusion limit the asymmetry is independent of time. These results are shown to apply to random walks in which individual steps have a stable law distribution as well as to multidimensional random walks.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 51 (1988), S. 215-232 
    ISSN: 1572-9613
    Schlagwort(e): Random walks ; diffusion processes ; first passage times ; residence times ; diffusive coherence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This paper discusses the simplest first passage time problems for random walks and diffusion processes on a line segment. When a diffusing particle moves in a time-varying field, use of the adjoint equation does not lead to any simplification in the calculation of moments of the first passage time as is the case for diffusion in a time-invariant field. We show that for a discrete random walk in the presence of a sinusoidally varying field there is a resonant frequency ϖ* for which the mean residence time on the line segment is a minimum. It is shown that for a random walk on a line segment of lengthL the mean residence time goes likeL 2 for largeL when ϖ≠ϖ*, but when ϖ=ϖ* the dependence is proportional toL. The results of our simulation are numerical, but can be regarded as exact. Qualitatively similar results are shown to hold for diffusion processes by a perturbation expansion in powers of a dimensionless velocity. These results are extended to higher values of this parameter by a numerical solution of the forward equation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    facet.materialart.
    Unbekannt
    In:  CASI
    Publikationsdatum: 2013-08-31
    Beschreibung: The Software Productivity Consortium is sponsored by 14 aerospace companies as a developer of software engineering methods and tools. Software reuse and prototyping are currently the major emphasis areas. The Methodology and Measurement Project in the Software Technology Exploration Division has developed some concepts for reuse which they intend to develop into a synthesis process. They have identified two approaches to software reuse: opportunistic and systematic. The assumptions underlying the systematic approach, phrased as hypotheses, are the following: the redevelopment hypothesis, i.e., software developers solve the same problems repeatedly; the oracle hypothesis, i.e., developers are able to predict variations from one redevelopment to others; and the organizational hypothesis, i.e., software must be organized according to behavior and structure to take advantage of the predictions that the developers make. The conceptual basis for reuse includes: program families, information hiding, abstract interfaces, uses and information hiding hierarchies, and process structure. The primary reusable software characteristics are black-box descriptions, structural descriptions, and composition and decomposition based on program families. Automated support can be provided for systematic reuse, and the Consortium is developing a prototype reuse library and guidebook. The software synthesis process that the Consortium is aiming toward includes modeling, refinement, prototyping, reuse, assessment, and new construction.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: NASA, Langley Research Center, Software Reuse Issues; p 67-88
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2019-06-28
    Beschreibung: The use of a decentralized approach to failure detection and isolation for use in restructurable control systems is examined. This work has produced: (1) A method for evaluating fundamental limits to FDI performance; (2) Application using flight recorded data; (3) A working control element FDI system with maximal sensitivity to critical control element failures; (4) Extensive testing on realistic simulations; and (5) A detailed design methodology involving parameter optimization (with respect to model uncertainties) and sensitivity analyses. This project has concentrated on detection and isolation of generic control element failures since these failures frequently lead to emergency conditions and since knowledge of remaining control authority is essential for control system redesign. The failures are generic in the sense that no temporal failure signature information was assumed. Thus, various forms of functional failures are treated in a unified fashion. Such a treatment results in a robust FDI system (i.e., one that covers all failure modes) but sacrifices some performance when detailed failure signature information is known, useful, and employed properly. It was assumed throughout that all sensors are validated (i.e., contain only in-spec errors) and that only the first failure of a single control element needs to be detected and isolated. The FDI system which has been developed will handle a class of multiple failures.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: NASA-CR-178213 , NAS 1.26:178213 , TR-309
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2017-10-02
    Beschreibung: The use of timing diagrams is recommended in the design and testing of multi-task Ada programs. By displaying the task states vs. time, timing diagrams can portray the simultaneous threads of data flow and control which characterize tasking programs. This description of the system's dynamic behavior from conception to testing is a necessary adjunct to other graphical techniques, such as structure charts, which essentially give a static view of the system. A series of steps is recommended which incorporates timing diagrams into the design process. Finally, a description is provided of a prototype Ada Execution Analyzer (AEA) which automates the production of timing diagrams from VAX/Ada debugger output.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: NASA, Lyndon B. Johnson Space Center, First International Conference on Ada (R) Programming Language Applications for the NASA Space Station, Volume 1; 11 p
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2019-06-28
    Beschreibung: Basili and Weiss (1984) have discussed an approach for obtaining valid data which may be used to evaluate software development methodologies in a production environment. The methodology consists of five elements, including the identification of goals, the determination of questions of interest from the goals, the development of a data collection form, the development of data collection procedures, and the validation and analysis of the data. The current investigation is concerned with the presentation of the results from such an evaluation. The presented data were collected as part of studies reported by Basili et al. (1977). These studies had been conducted by NASA's Software Engineering Laboratory (SEL). Attention is given to an overview of the SEL, the application of the considered methodology, the results of a data analysis, and conclusions about the SEL environment.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: IEEE Transactions on Software Engineering (ISSN 0098-5589); SE-11; 157-168
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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