664 research outputs found
Stabilizing Consensus Is Impossible in Lossy Iterated Immediate Snapshot Models
No full textA substantial portion of distributed computing research is dedicated to terminating problems like consensus and similar agreement problems. However, non-terminating problems have been intensively studied in the context of self-stabilizing distributed algorithms, where processes may start from arbitrary initial states and can tolerate arbitrary transient faults. In between lie stabilizing problems, where the processes start from a well-defined initial state, but do not need to decide irrevocably and are allowed to change their decision finitely often until a stable decision is eventually reached.
Stabilizing consensus has been studied within the context of synchronous message adversaries. In particular, Charron-Bost and Moran showed that a necessary condition for stabilizing consensus is the existence of at least one process that reaches all others infinitely often (a perpetual broadcaster). However, it was left open whether this is also a sufficient condition for solving stabilizing consensus.
In this paper, we introduce the novel Delayed Lossy-Link (DLL) model, and the Lossy Iterated Immediate Snapshot Model (LIIS), for which we show stabilizing consensus to be impossible. The DLL model is introduced as a variant of the well-known Lossy-Link model, which admits silence periods of arbitrary but finite length. The LIIS model is a variant of the Iterated Immediate Snapshot (IIS), model which admits finite length periods of at most f omission faults per layer. In particular, we show that stabilizing consensus is impossible even when f = 1.
Our results show that even in a model with very strong connectivity, namely, the Iterated Immediate Snapshot (IIS) model, a single omission fault per layer effectively disables stabilizing consensus. Furthermore, since the DLL model always has a perpetual broadcaster, the mere existence of a perpetual broadcaster, even in a crash-free setting, is not sufficient for solving stabilizing consensus, negatively answering the open question posed by Charron-Bost and Moran
Long-Term Stable Microwave Signal Extraction from Mode-Locked Lasers
No full textLong-term synchronization between two 10.225 GHz microwave signals at + 10 dBm power level, locked to a 44.26 MHz repetition rate passively mode-locked fiber laser, is demonstrated using balanced optical-microwave phase detectors. The out-of-loop measurement result shows 12.8 fs relative timing jitter integrated from 10 Hz to 10 MHz. Long-term timing drift measurement shows 48 fs maximum deviation over one hour, mainly limited by drift of the out-of-loop characterization setup itself. To the best of our knowledge, this is the first time to demonstrate long-term (> 1 hour) 3 mrad-level phase stability of a 10.225 GHz microwave signal extracted from a mode-locked laser. (c) 2007 Optical Society of America
A.P. Bagliane, F. Santi (éd.) : Social and Cultural Attitudes to Epidemics in the late Middle Ages. A. Paravicini Bagliani, J. P. Felber, J.D. Morerod, V. Pasche (sous la direction de) : Les Pays Romands au Moyen Age.
No full textA.P. Bagliane, F. Santi (éd.) : Social and Cultural Attitudes to Epidemics in the late Middle Ages. A. Paravicini Bagliani, J. P. Felber, J.D. Morerod, V. Pasche (sous la direction de) : Les Pays Romands au Moyen Age.. In: Revue de géographie alpine, tome 86, n°2, 1998. p. 125
A.P. Bagliane, F. Santi (éd.) : Social and Cultural Attitudes to Epidemics in the late Middle Ages. A. Paravicini Bagliani, J. P. Felber, J.D. Morerod, V. Pasche (sous la direction de) : Les Pays Romands au Moyen Age.
No full textA.P. Bagliane, F. Santi (éd.) : Social and Cultural Attitudes to Epidemics in the late Middle Ages. A. Paravicini Bagliani, J. P. Felber, J.D. Morerod, V. Pasche (sous la direction de) : Les Pays Romands au Moyen Age.. In: Revue de géographie alpine, tome 86, n°2, 1998. p. 125
Il fenomeno carsico del comprensorio Monte San Giorgio – Orsa – Pravello (Svizzera – Italia): censimento e descrizione delle cavità
No full textAfter the goldrush : Joe Felber, Sasha Grbich, Lisa Harms
No full textCatalogue of an exhibition held at SASA Gallery, Adelaide, 5 May-5 June 2009.Artist: Lisa Harms.
Editor: Mary Knights.
Includes bibliographical references
Immunoreactive ACTH and cortisol plasma levels during pregnancy. Detection and partial purification of corticotrophin-like placental hormone: the human chorionic corticotrophin (HCC).
No full textThe high plasma cortisol and ACTH levels present in pregnant women as well as the non-parrallelism of their plasma extract dilution curves in comparison with the standard curve in the ACTH radioimmunoassay, are evidence for the presence of an ACTH-like substance during pregnancy which would interfere with the assay. Placental extracts were obtained by acid-acetone extraction, followed by partial purification with oxycellulose and by extraction with porous glass powder. A substance was detected which partially cross-reacted with synthetic human ACTH in the radioimmunoassay and which showed biological activity using the assay procedure described by Liscomb & Nelson. The data sustain the existence of an ACTH-like placental hormone: human chorionic corticotrophin (HCC)
Theoretical and practical limitations of the acetylene inhibition technique to determine total denitrification losses
No full textThe loss of N2 from intensively managed agro-ecosystems is an important part of the N budget. Flux monitoring of N2 emissions at the field scale, e.g., by eddy correlation or aerodynamic gradient method, is impossible due to the large atmospheric N2 background (78%). The acetylene (C2H2) inhibition technique (AIT) is a rather simple and frequently used, albeit imperfect, method to determine N2 losses from intact soil cores. In principle, AIT allows an estimation of total denitrification at high temporal resolution and on small spatial scales, with limited workload and costs involved. To investigate its potential and limitations, a laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed simultaneous measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with automated C2H2 injection. A survey of total denitrification losses (N2 + N2O) over 1.5 yr in soil cores from an intensively managed, cut grassland system in central Switzerland supports previous reports on severe limitations of the AIT, which precluded reliable estimates of total denitrification losses. Further, the unavoidable sampling and transfer of soil samples to the laboratory causes unpredictable deviations from the denitrification activity in the field
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