43,570 research outputs found
FORTRAN programming - A self-taught course
Comprehensive programming course begins with numerical systems and basic concepts, proceeds systematically through FORTRAN language elements, and concludes with discussion of programming techniques. Course is suitable either for individual study or for group study on informal basis
Monte Carlo analysis of uncertainty propagation in a stratospheric model. 1: Development of a concise stratospheric model
A concise model has been developed to analyze uncertainties in stratospheric perturbations, yet uses a minimum of computer time and is complete enough to represent the results of more complex models. The steady state model applies iteration to achieve coupling between interacting species. The species are determined from diffusion equations with appropriate sources and sinks. Diurnal effects due to chlorine nitrate formation are accounted for by analytic approximation. The model has been used to evaluate steady state perturbations due to injections of chlorine and NO(X)
Monte Carlo analysis of uncertainty propagation in a stratospheric model. 2: Uncertainties due to reaction rates
A concise stratospheric model was used in a Monte-Carlo analysis of the propagation of reaction rate uncertainties through the calculation of an ozone perturbation due to the addition of chlorine. Two thousand Monte-Carlo cases were run with 55 reaction rates being varied. Excellent convergence was obtained in the output distributions because the model is sensitive to the uncertainties in only about 10 reactions. For a 1 ppby chlorine perturbation added to a 1.5 ppby chlorine background, the resultant 1 sigma uncertainty on the ozone perturbation is a factor of 1.69 on the high side and 1.80 on the low side. The corresponding 2 sigma factors are 2.86 and 3.23. Results are also given for the uncertainties, due to reaction rates, in the ambient concentrations of stratospheric species
The output distribution of important LULU-operators
Two procedures to compute the output distribution phi_S of certain stack
filters S (so called erosion-dilation cascades) are given. One rests on the
disjunctive normal form of S and also yields the rank selection probabilities.
The other is based on inclusion-exclusion and e.g. yields phi_S for some
important LULU-operators S. Properties of phi_S can be used to characterize
smoothing properties of S. One of the methods discussed also allows for the
calculation of the reliability polynomial of any positive Boolean function
(e.g. one derived from a connected graph).Comment: 20 pages, up to trivial differences this is the final version to be
published in Quaestiones Mathematicae 201
Synchronization and fault-masking in redundant real-time systems
A real time computer may fail because of massive component failures or not responding quickly enough to satisfy real time requirements. An increase in redundancy - a conventional means of improving reliability - can improve the former but can - in some cases - degrade the latter considerably due to the overhead associated with redundancy management, namely the time delay resulting from synchronization and voting/interactive consistency techniques. The implications of synchronization and voting/interactive consistency algorithms in N-modular clusters on reliability are considered. All these studies were carried out in the context of real time applications. As a demonstrative example, we have analyzed results from experiments conducted at the NASA Airlab on the Software Implemented Fault Tolerance (SIFT) computer. This analysis has indeed indicated that in most real time applications, it is better to employ hardware synchronization instead of software synchronization and not allow reconfiguration
Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions
By use of first-principles electronic structure calculations, we predict that
the magnetoresistance of the bcc Co(100)/MgO(100)/bcc Co(100) and
FeCo(100)/MgO(100)/FeCo(100) tunneling junctions can be several times larger
than the very large magnetoresistance predicted for the
Fe(100)/MgO(100)/Fe(100) system. The origin of this large magnetoresistance can
be understood using simple physical arguments by considering the electrons at
the Fermi energy travelling perpendicular to the interfaces. For the minority
spins there is no state with symmetry whereas for the majority spins
there is only a state. The state decays much more slowly
than the other states within the MgO barrier. In the absence of scattering
which breaks the conservation of momentum parallel to the interfaces, the
electrons travelling perpendicular to the interfaces undergo total reflection
if the moments of the electrodes are anti-parallel. These arguments apply
equally well to systems with other well ordered tunnel barriers and for which
the most slowly decaying complex energy band in the barrier has
symmetry. Examples include systems with (100) layers constructed from Fe, bcc
Co, or bcc FeCo electrodes and Ge, GaAs, or ZnSe barriers.Comment: 8 figure files in eps forma
From Event-B models to Dafny code contracts
International audienceThe constructive approach to software correctness aims at formal modelling and verification of the structure and behaviour of a system in different levels of abstraction. In contrast, the analytical approach to software verification focuses on code level correctness and its verification. Therefore it would seem that the constructive and analytical approaches should complement each other well. To demonstrate this idea we present a case for linking two existing verification methods, Event-B (constructive) and Dafny (analytical). This approach combines the power of Event-B abstraction and its stepwise refinement with the verification capabilities of Dafny. We presented a small case study to demonstrate this approach and outline of the rules for transforming Event-B events to Dafny contracts. Finally, a tool for automatic generation of Dafny contracts from Event-B formal models is presented
Exploring Io's atmospheric composition with APEX: first measurement of 34SO2 and tentative detection of KCl
The composition of Io's tenuous atmosphere is poorly constrained. Only the
major species SO2 and a handful of minor species have been positively
identified, but a variety of other molecular species should be present, based
on thermochemical equilibrium models of volcanic gas chemistry and the
composition of Io's environment. This paper focuses on the spectral search for
expected yet undetected molecular species (KCl, SiO, S2O) and isotopes (34SO2).
We analyze a disk-averaged spectrum of a potentially line-rich spectral window
around 345 GHz, obtained in 2010 at the APEX-12m antenna (Atacama Pathfinder
EXperiment). Using different models assuming either extended atmospheric
distributions or a purely volcanically-sustained atmosphere, we tentatively
measure the KCl relative abundance with respect to SO2 and derive a range of
4x10^{-4}-8x10^{-3}. We do not detect SiO or S2O and present new upper limits
on their abundances. We also present the first measurement of the 34S/32S
isotopic ratio in gas phase on Io, which appears to be twice as high as the
Earth and ISM reference values. Strong lines of SO2 and SO are also analyzed to
check for longitudinal variations of column density and relative abundance. Our
models show that, based on their predicted relative abundance with respect to
SO2 in volcanic plumes, both the tentative KCl detection and SiO upper limit
are compatible with a purely volcanic origin for these species.Comment: Accepted for publication in ApJ. 11 pages, 4 figure
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