35,048 research outputs found
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
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
The composition of Event-B models
The transition from classical B [2] to the Event-B language and method [3] has seen the removal of some forms of model structuring and composition, with the intention of reinventing them in future. This work contributes to thatreinvention. Inspired by a proposed method for state-based decomposition and refinement [5] of an Event-B model, we propose a familiar parallel event composition (over disjoint state variable lists), and the less familiar event fusion (over intersecting state variable lists). A brief motivation is provided for these and other forms of composition of models, in terms of feature-based modelling. We show that model consistency is preserved under such compositions. More significantly we show that model composition preserves refinement
A Calculus for Orchestration of Web Services
We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been influenced by WS-BPEL, the de facto standard language for orchestration of web services. COWS combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different from any of them. Several examples illustrates COWS peculiarities and show its expressiveness both for modelling imperative and orchestration constructs, e.g. web services, flow graphs, fault and compensation handlers, and for encoding other process and orchestration languages
Planck Low Frequency Instrument: Beam Patterns
The Low Frequency Instrument on board the ESA Planck satellite is coupled to
the Planck 1.5 meter off-axis dual reflector telescope by an array of 27
corrugated feed horns operating at 30, 44, 70, and 100 GHz. We briefly present
here a detailed study of the optical interface devoted to optimize the angular
resolution (10 arcmin at 100 GHz as a goal) and at the same time to minimize
all the systematics coming from the sidelobes of the radiation pattern. Through
optical simulations, we provide shapes, locations on the sky, angular
resolutions, and polarization properties of each beam.Comment: On behalf of the Planck collaboration. 3 pages, 1 figure. Article
published in the Proceedings of the 2K1BC Experimental Cosmology at
millimetre wavelength
The Planck Low Frequency Instrument
The Low Frequency Instrument (LFI) of the "Planck Surveyor" ESA mission will
perform high-resolution imaging of the Cosmic Microwave Background anisotropies
at four frequencies in the 30-100 GHz range. We review the LFI main scientific
objectives, the current status of the instrument design and the on-going effort
to develop software simulations of the LFI observations. In particular we
discuss the design status of the PLANCK telescope, which is critical for
reaching adequate effective angular resolution.Comment: 10 pages, Latex (use epsfig.sty); 4 Postscript figures; Astrophys.
Lett & Comm, in press. Proc. of the Conference: "The Cosmic Microwave
Background and the Planck Mission", Santander, Spain, 22-25 June 199
A theoretical study of the C- 4So_3/2 and 2Do_{3/2,5/2} bound states and C ground configuration: fine and hyperfine structures, isotope shifts and transition probabilities
This work is an ab initio study of the 2p3 4So_3/2, and 2Do_{3/2,5/2} states
of C- and 2p2 3P_{0,1,2}, 1D_2, and 1S_0 states of neutral carbon. We use the
multi-configuration Hartree-Fock approach, focusing on the accuracy of the wave
function itself. We obtain all C- detachment thresholds, including correlation
effects to about 0.5%. Isotope shifts and hyperfine structures are calculated.
The achieved accuracy of the latter is of the order of 0.1 MHz.
Intra-configuration transition probabilities are also estimated.Comment: 15 pages, 2 figures, 12 table
Quenching Effects in the Hadron Spectrum
Lattice QCD has generated a wealth of data in hadronic physics over the last
two decades. Until relatively recently, most of this information has been
within the "quenched approximation" where virtual quark--anti-quark pairs are
neglected. This review presents a descriptive discussion of the effects of
removing this approximation in the calculation of hadronic masses.Comment: To appear in "Lattice Hadron Physics", ed. A.C. Kalloniatis, D.B.
Leinweber and A.G. William
Metabolites, Metabolic Hormones and Hematological Profiles in Mountain Goats Before the Breeding Season and During the First Trimester of Pregnancy
Objectives were to evaluate the relationships among energy-related metabolites, hormones, and hematological variables in mountain goats (Oreamnos Americans) before the breeding season and during the 1st trimester of pregnancy. Does were from herds in the Palisades (PAL) and NE Yellowstone (NEY) areas. Samples were collected from July to Aug. (before breeding season) and mid-Jan. (1st trimester of pregnancy). Sera was assayed for insulin (I), thyroxine (T4), triiodothyronine (T3), b-OH-butyrate (bOHB), blood urea nitrogen (BUN), and total protein (TP). Concentrations of TP did not differ (P > 0.05) between pregnant (P) and non-breeding season (NB) does. bOHB, I, BUN, and T3 concentrations, and the T3:T4 ratios were greater (P < 0.05) in NB does than in P does. Whereas, T4 concentrations were greater (P < 0.05) in P does than in NB does. Obviously, NB does have a different profiles of metabolites, metabolic hormones and select hematological variables compared to P does.Ā In conclusion, these differences may be related to P does utilizing and partitioning nutrients to support placental and fetal growth and development. These differences may also be related to the effect of season, since there were no non-pregnant does were sampled in Jan. Another factor that may be important for interpretation of these differences is location. All NB does were sampled in the PAL, while all P does were sampled in the NEY
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