Roger M. Kieckhafer

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This paper describes the Multicomputer Architecture for Fault-Tolerance (MAFT), a distributed system designed to provide extremely reliable computation in real-time control systems. MAFT is based on the physical and functional partitioning of executive functions from application functions. The implementation of the executive functions in a special-purpose(More)
ÐIn a fault-tolerant distributed system, it is often necessary for nonfaulty processes to agree on the value of a shared data item. The criterion of Approximate Agreement does not require processes to achieve exact agreement on a value; rather, they need only agree to within a predefined numerical tolerance. Approximate Agreement can be achieved through(More)
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 x 10(19) electron volts and the positions of active galactic nuclei (AGN) lying within approximately 75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these(More)
An important problem in fault-tolerant distributed systems is maintaining agreement between nonfaulty processes in the presence of undiagnosed faults. To achieve agreement, processes exchange their local “opinions” of a particular value, and then vote on the values received to arrive at a “consensus.” Approximate Agreement defines a condition in which it is(More)
Firewalls form the first line of defense in securing internal networks from the Internet. A Firewall only provides security if all traffic into and out of an internal network passes through the firewall. However, a single firewall through which all network traffic must flow represents a single point of failure. If the firewall is down, all access is lost. A(More)
This paper concerns the problem of scheduling instability, where reducing the duration of one or more tasks delays the starting time of another task. This can make it difficult or impossible to guarantee real-time deadlines. Unfortunately, simulating schedules with all possible variations in the durations of all tasks is in most cases an intractable(More)
The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and(More)
The energy spectrum of cosmic rays above 2.5 x 10;{18} eV, derived from 20,000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional, variantE;{-gamma}, at energies between 4 x 10;{18} eV and 4 x 10;{19} eV is 2.69+/-0.02(stat)+/-0.06(syst), steepening to 4.2+/-0.4(stat)+/-0.06(syst) at(More)