The Experts below are selected from a list of 828 Experts worldwide ranked by ideXlab platform
Mark A Clilverd - One of the best experts on this subject based on the ideXlab platform.
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Remote sensing space weather events: the AARDDVARK network
2014Co-Authors: Mark A Clilverd, Craig J. Rodger, Neil R Thomson, J B Brundell, Pekka T. Verronen, Esa TurunenAbstract:Abstract. The Antarctic-Arctic Radiation-belt (Dynamic) Deposition- VLF Atmospheric Research Konsortium (AARDDVARK) provides a network of continuous long-range observations of the lower-ionosphere in the polar regions. Our ultimate aim is to develop the network of sensors to detect changes in ionization levels from ~30-90 km altitude, globally, continuously, and with high time resolution, with the goal of increasing the understanding of energy coupling between the Earth's atmosphere, the Sun, and space. This science area impacts our knowledge of space weather processes, global atmospheric change, communications, and navigation. The joint New Zealand-United Kingdom AARDDVARK is a new extension of a well-established experimental technique, allowing long-range probing of ionization changes at comparatively low altitudes. Most other instruments which can probe the same altitudes are limited to essentially overhead measurements. At this stage AARDDVARK is essentially unique, as similar systems are only deployed at a regional level. The AARDDVARK network has contributed to the scientific understanding of a growing list of space weather science topics including solar proton events, the descent of NOx into the middle atmosphere, substorms, precipitation of energetic electrons by plasmaspheric hiss and EMIC waves, the impact of coronal mass ejections upon the radiation belts, and relativistic electron microbursts. Future additions to the receiver network will increase the science potential and provide global coverage of space weather event signatures
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a statistical approach to determining energetic outer radiation belt electron precipitation fluxes
Journal of Geophysical Research, 2014Co-Authors: Mea Simon Wedlund, E Spanswick, Craig J. Rodger, Paul Breen, Mark A Clilverd, J V Rodriguez, Kathy Cresswellmoorcock, Neil Cobbett, D W DanskinAbstract:Subionospheric radio wave data from an Antarctic-Arctic Radiation-Belt (Dynamic) Deposition VLF Atmospheric Research Konsortia (AARDDVARK) receiver located in Churchill, Canada, is analyzed to determine the characteristics of electron precipitation into the atmosphere over the range 3 30 keV precipitation flux determined by the AARDDVARK technique was found to be ±10%. Peak >30 keV precipitation fluxes of AARDDVARK-derived precipitation flux during the main and recovery phase of the largest geomagnetic storm, which started on 4 August 2010, were >105 el cm−2 s−1 sr−1. The largest fluxes observed by AARDDVARK occurred on the dayside and were delayed by several days from the start of the geomagnetic disturbance. During the main phase of the disturbances, nightside fluxes were dominant. Significant differences in flux estimates between POES, AARDDVARK, and the riometer were found after the main phase of the largest disturbance, with evidence provided to suggest that >700 keV electron precipitation was occurring. Currently the presence of such relativistic electron precipitation introduces some uncertainty in the analysis of AARDDVARK data, given the assumption of a power law electron precipitation spectrum.
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the plasmasphere during a space weather event first results from the plasmon project
Journal of Space Weather and Space Climate, 2013Co-Authors: Craig J. Rodger, Mark A Clilverd, Janos Lichtenberger, A B Collier, Balazs Heilig, M Vellante, J Manninen, A M Jorgensen, Jan RedaAbstract:The results of the first 18 months of the PLASMON project are presented. We have extended our three, existing ground-based measuring networks, AWDANet (VLF/whistlers), EMMA/SANSA (ULF/FLRs), and AARDDVARK (VLF/perturbations on transmitters’ signal), by three, eight, and four new stations, respectively. The extended networks will allow us to achieve the four major scientific goals, the automatic retrieval of equatorial electron densities and density profiles of the plasmasphere by whistler inversion, the retrieval of equatorial plasma mass densities by EMMA and SANSA from FLRs, developing a new, data assimilative model of plasmasphere and validating the model predictions through comparison of modeled REP losses with measured data by AARDDVARK network. The first results on each of the four objectives are presented through a case study on a space weather event, a dual storm sudden commencement which occurred on August 3 and 4, 2010.
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remote sensing space weather events antarctic arctic radiation belt dynamic deposition vlf atmospheric research konsortium network
Social Work, 2009Co-Authors: Mark A Clilverd, Craig J. Rodger, Neil Cobbett, Neil R Thomson, J B Brundell, Thomas Ulich, Janos Lichtenberger, A B Collier, F W Menk, Annika SeppalaAbstract:[1] The Antarctic-Arctic Radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium (AARDDVARK) provides a network of continuous long-range observations of the lower ionosphere in the polar regions. Our ultimate aim is to develop the network of sensors to detect changes in ionization levels from ∼30–90 km altitude, globally, continuously, and with high time resolution, with the goal of increasing the understanding of energy coupling between the Earth's atmosphere, the Sun, and space. This science area impacts our knowledge of space weather processes, global atmospheric change, communications, and navigation. The joint New Zealand-United Kingdom AARDDVARK is a new extension of a well-established experimental technique, allowing long-range probing of ionization changes at comparatively low altitudes. Most other instruments which can probe the same altitudes are limited to essentially overhead measurements. At this stage AARDDVARK is essentially unique, as similar systems are only deployed at a regional level. The AARDDVARK network has contributed to the scientific understanding of a growing list of space weather science topics including solar proton events, the descent of NOx into the middle atmosphere, substorms, precipitation of energetic electrons by plasmaspheric hiss and electromagnetic ion cyclotron waves, the impact of coronal mass ejections upon the radiation belts, and relativistic electron microbursts. Future additions to the receiver network will increase the science potential and provide global coverage of space weather event signatures.
Michael Buckley - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Collagen Sequence Analysis of the Extinct Giant Ground Sloths Lestodon and
2016Co-Authors: Michael Buckley, Richard A. Fariña, Craig Lawless, Sebastián P. Tambusso, Luciano Varela, Alfredo A. Carlini, Jaime E. Powell, Jorge G. MartinezAbstract:For over 200 years, fossils of bizarre extinct creatures have been described from the Ameri-cas that have ranged from giant ground sloths to the ‘native ’ South American ungulates, groups of mammals that evolved in relative isolation on South America. Ground sloths belong to the South American xenarthrans, a group with modern although morphologically and ecologically very different representatives (anteaters, armadillos and sloths), which has been proposed to be one of the four main eutherian clades. Recently, proteomics analyses of bone collagen have recently been used to yield a molecular phylogeny for a range of mammals including the unusual ‘Malagasy Aardvark ’ shown to be most closely related to the afrotherian tenrecs, and the south American ungulates supporting their morphological association with condylarths. However, proteomics results generate partial sequence infor-mation that could impact upon the phylogenetic placement that has not been appropriately tested. For comparison, this paper examines the phylogenetic potential of proteomics-based sequencing through the analysis of collagen extracted from two extinct giant ground sloths, Lestodon andMegatherium. The ground sloths were placed as sister taxa to extan
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Collagen Sequence Analysis of the Extinct Giant Ground Sloths Lestodon and Megatherium
2015Co-Authors: Michael Buckley, Richard A. Fariña, Craig Lawless, Sebastián P. Tambusso, Luciano Varela, Alfredo A. Carlini, Jaime E. Powell, Jorge G. MartinezAbstract:For over 200 years, fossils of bizarre extinct creatures have been described from the Americas that have ranged from giant ground sloths to the ‘native’ South American ungulates, groups of mammals that evolved in relative isolation on South America. Ground sloths belong to the South American xenarthrans, a group with modern although morphologically and ecologically very different representatives (anteaters, armadillos and sloths), which has been proposed to be one of the four main eutherian clades. Recently, proteomics analyses of bone collagen have recently been used to yield a molecular phylogeny for a range of mammals including the unusual ‘Malagasy Aardvark’ shown to be most closely related to the afrotherian tenrecs, and the south American ungulates supporting their morphological association with condylarths. However, proteomics results generate partial sequence information that could impact upon the phylogenetic placement that has not been appropriately tested. For comparison, this paper examines the phylogenetic potential of proteomics-based sequencing through the analysis of collagen extracted from two extinct giant ground sloths, Lestodon and Megatherium. The ground sloths were placed as sister taxa to extant sloths, but with a closer relationship between Lestodon and the extant sloths than the basal Megatherium. These results highlight that proteomics methods could yield plausible phylogenies that share similarities with other methods, but have the potential to be more useful in fossils beyond the limits of ancient DNA survival.
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MALDI-ToF-MS spectra of collagen digests from the sub-fossil ‘malagasy Aardvark’ Plesiorycteropus and modern specimens.
2013Co-Authors: Michael BuckleyAbstract:The peptide mass fingerprints (PMFs) show that the quality of the collagen extracted from the fossil is as good as from modern specimens (from top to bottom; Aardvark (Orycteropus afer), Plesiorycteropus sp., rock hyrax (Procavia capensis) and greater hedgehog tenrec (Setifer setosus)). Peaks marked α and β represent some of the most variable homologous peptides manually sequenced (Fig. 3 & Fig. S2). A greater similarity between peptide m/z values can be seen between Plesiorycteropus and tenrec than any other species sampled.
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Example tandem MS spectra of three homologous peptides.
2013Co-Authors: Michael BuckleyAbstract:The spectra are from peptide COL1A2495–509 (peak ‘α’ in Fig. 2) with precursor (MH+) ions at (from top to bottom) m/z 1453 (elephants, pangolin anteater and tamandua), 1463 (hyrax and Aardvark) and 1477 (armadillos and all afrosoricids including the extinct Plesiorycteropus). Labeling of fragment ions (inset) follows [37], underline represents hydroxylation site, red text highlights amino acids that differ from the inset (elephant, anteater & pangolin) sequence. Isobaric amino acids (I/L) were estimated based on conserved DNA sequence data where possible; for sites that have more than one isobaric amino acid present, the most abundant was used (see Supplementary Information).
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A Molecular Phylogeny of Plesiorycteropus Reassigns the Extinct Mammalian Order ‘Bibymalagasia’. Plos One 8(3):e59614. doi: 10.1371/journal.pone.0059614 PMID: 23555726
2013Co-Authors: Michael BuckleyAbstract:Madagascar is well known for its diverse fauna and flora, being home to many species not found anywhere else in the world. However, its biodiversity in the recent past included a range of extinct enigmatic fauna, such as elephant birds, giant lemurs and dwarfed hippopotami. The ‘Malagasy Aardvark ’ (Plesiorycteropus) has remained one of Madagascar’s least well-understood extinct species since its discovery in the 19th century. Initially considered a close relative of the Aardvark (Orycteropus) within the order Tubulidentata, more recent morphological analyses challenged this placement on the grounds that the identifiably derived traits supporting this allocation were adaptations to digging rather than shared ancestry. Because the skeletal evidence showed many morphological traits diagnostic of different eutherian mammal orders, they could not be used to resolve its closest relatives. As a result, the genus was tentatively assigned its own taxonomic order ‘Bibymalagasia’, yet how this order relates to other eutherian mammal orders remains unclear despite numerous morphological investigations. This research presents the first known molecular sequence data for Plesiorycteropus, obtained from the bone protein collagen (I), which places the ‘Malagasy Aardvark ’ as more closely related to tenrecs than Aardvarks. More specifically, Plesiorycteropus was recovered within the order Tenrecoidea (golden moles and tenrecs) within Afrotheria, suggesting that the taxonomic order ‘Bibymalagasia ’ is obsolete. This research highlights the potential for collagen sequencing in investigating the phylogeny of extinct species as a viable alternative to ancient DNA (aDNA) sequencing, particularly in cases where aDNA cannot be recovered
Craig J. Rodger - One of the best experts on this subject based on the ideXlab platform.
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Remote sensing space weather events: the AARDDVARK network
2014Co-Authors: Mark A Clilverd, Craig J. Rodger, Neil R Thomson, J B Brundell, Pekka T. Verronen, Esa TurunenAbstract:Abstract. The Antarctic-Arctic Radiation-belt (Dynamic) Deposition- VLF Atmospheric Research Konsortium (AARDDVARK) provides a network of continuous long-range observations of the lower-ionosphere in the polar regions. Our ultimate aim is to develop the network of sensors to detect changes in ionization levels from ~30-90 km altitude, globally, continuously, and with high time resolution, with the goal of increasing the understanding of energy coupling between the Earth's atmosphere, the Sun, and space. This science area impacts our knowledge of space weather processes, global atmospheric change, communications, and navigation. The joint New Zealand-United Kingdom AARDDVARK is a new extension of a well-established experimental technique, allowing long-range probing of ionization changes at comparatively low altitudes. Most other instruments which can probe the same altitudes are limited to essentially overhead measurements. At this stage AARDDVARK is essentially unique, as similar systems are only deployed at a regional level. The AARDDVARK network has contributed to the scientific understanding of a growing list of space weather science topics including solar proton events, the descent of NOx into the middle atmosphere, substorms, precipitation of energetic electrons by plasmaspheric hiss and EMIC waves, the impact of coronal mass ejections upon the radiation belts, and relativistic electron microbursts. Future additions to the receiver network will increase the science potential and provide global coverage of space weather event signatures
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a statistical approach to determining energetic outer radiation belt electron precipitation fluxes
Journal of Geophysical Research, 2014Co-Authors: Mea Simon Wedlund, E Spanswick, Craig J. Rodger, Paul Breen, Mark A Clilverd, J V Rodriguez, Kathy Cresswellmoorcock, Neil Cobbett, D W DanskinAbstract:Subionospheric radio wave data from an Antarctic-Arctic Radiation-Belt (Dynamic) Deposition VLF Atmospheric Research Konsortia (AARDDVARK) receiver located in Churchill, Canada, is analyzed to determine the characteristics of electron precipitation into the atmosphere over the range 3 30 keV precipitation flux determined by the AARDDVARK technique was found to be ±10%. Peak >30 keV precipitation fluxes of AARDDVARK-derived precipitation flux during the main and recovery phase of the largest geomagnetic storm, which started on 4 August 2010, were >105 el cm−2 s−1 sr−1. The largest fluxes observed by AARDDVARK occurred on the dayside and were delayed by several days from the start of the geomagnetic disturbance. During the main phase of the disturbances, nightside fluxes were dominant. Significant differences in flux estimates between POES, AARDDVARK, and the riometer were found after the main phase of the largest disturbance, with evidence provided to suggest that >700 keV electron precipitation was occurring. Currently the presence of such relativistic electron precipitation introduces some uncertainty in the analysis of AARDDVARK data, given the assumption of a power law electron precipitation spectrum.
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the plasmasphere during a space weather event first results from the plasmon project
Journal of Space Weather and Space Climate, 2013Co-Authors: Craig J. Rodger, Mark A Clilverd, Janos Lichtenberger, A B Collier, Balazs Heilig, M Vellante, J Manninen, A M Jorgensen, Jan RedaAbstract:The results of the first 18 months of the PLASMON project are presented. We have extended our three, existing ground-based measuring networks, AWDANet (VLF/whistlers), EMMA/SANSA (ULF/FLRs), and AARDDVARK (VLF/perturbations on transmitters’ signal), by three, eight, and four new stations, respectively. The extended networks will allow us to achieve the four major scientific goals, the automatic retrieval of equatorial electron densities and density profiles of the plasmasphere by whistler inversion, the retrieval of equatorial plasma mass densities by EMMA and SANSA from FLRs, developing a new, data assimilative model of plasmasphere and validating the model predictions through comparison of modeled REP losses with measured data by AARDDVARK network. The first results on each of the four objectives are presented through a case study on a space weather event, a dual storm sudden commencement which occurred on August 3 and 4, 2010.
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remote sensing space weather events antarctic arctic radiation belt dynamic deposition vlf atmospheric research konsortium network
Social Work, 2009Co-Authors: Mark A Clilverd, Craig J. Rodger, Neil Cobbett, Neil R Thomson, J B Brundell, Thomas Ulich, Janos Lichtenberger, A B Collier, F W Menk, Annika SeppalaAbstract:[1] The Antarctic-Arctic Radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium (AARDDVARK) provides a network of continuous long-range observations of the lower ionosphere in the polar regions. Our ultimate aim is to develop the network of sensors to detect changes in ionization levels from ∼30–90 km altitude, globally, continuously, and with high time resolution, with the goal of increasing the understanding of energy coupling between the Earth's atmosphere, the Sun, and space. This science area impacts our knowledge of space weather processes, global atmospheric change, communications, and navigation. The joint New Zealand-United Kingdom AARDDVARK is a new extension of a well-established experimental technique, allowing long-range probing of ionization changes at comparatively low altitudes. Most other instruments which can probe the same altitudes are limited to essentially overhead measurements. At this stage AARDDVARK is essentially unique, as similar systems are only deployed at a regional level. The AARDDVARK network has contributed to the scientific understanding of a growing list of space weather science topics including solar proton events, the descent of NOx into the middle atmosphere, substorms, precipitation of energetic electrons by plasmaspheric hiss and electromagnetic ion cyclotron waves, the impact of coronal mass ejections upon the radiation belts, and relativistic electron microbursts. Future additions to the receiver network will increase the science potential and provide global coverage of space weather event signatures.
Janos Lichtenberger - One of the best experts on this subject based on the ideXlab platform.
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the plasmasphere during a space weather event first results from the plasmon project
Journal of Space Weather and Space Climate, 2013Co-Authors: Craig J. Rodger, Mark A Clilverd, Janos Lichtenberger, A B Collier, Balazs Heilig, M Vellante, J Manninen, A M Jorgensen, Jan RedaAbstract:The results of the first 18 months of the PLASMON project are presented. We have extended our three, existing ground-based measuring networks, AWDANet (VLF/whistlers), EMMA/SANSA (ULF/FLRs), and AARDDVARK (VLF/perturbations on transmitters’ signal), by three, eight, and four new stations, respectively. The extended networks will allow us to achieve the four major scientific goals, the automatic retrieval of equatorial electron densities and density profiles of the plasmasphere by whistler inversion, the retrieval of equatorial plasma mass densities by EMMA and SANSA from FLRs, developing a new, data assimilative model of plasmasphere and validating the model predictions through comparison of modeled REP losses with measured data by AARDDVARK network. The first results on each of the four objectives are presented through a case study on a space weather event, a dual storm sudden commencement which occurred on August 3 and 4, 2010.
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remote sensing space weather events antarctic arctic radiation belt dynamic deposition vlf atmospheric research konsortium network
Social Work, 2009Co-Authors: Mark A Clilverd, Craig J. Rodger, Neil Cobbett, Neil R Thomson, J B Brundell, Thomas Ulich, Janos Lichtenberger, A B Collier, F W Menk, Annika SeppalaAbstract:[1] The Antarctic-Arctic Radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium (AARDDVARK) provides a network of continuous long-range observations of the lower ionosphere in the polar regions. Our ultimate aim is to develop the network of sensors to detect changes in ionization levels from ∼30–90 km altitude, globally, continuously, and with high time resolution, with the goal of increasing the understanding of energy coupling between the Earth's atmosphere, the Sun, and space. This science area impacts our knowledge of space weather processes, global atmospheric change, communications, and navigation. The joint New Zealand-United Kingdom AARDDVARK is a new extension of a well-established experimental technique, allowing long-range probing of ionization changes at comparatively low altitudes. Most other instruments which can probe the same altitudes are limited to essentially overhead measurements. At this stage AARDDVARK is essentially unique, as similar systems are only deployed at a regional level. The AARDDVARK network has contributed to the scientific understanding of a growing list of space weather science topics including solar proton events, the descent of NOx into the middle atmosphere, substorms, precipitation of energetic electrons by plasmaspheric hiss and electromagnetic ion cyclotron waves, the impact of coronal mass ejections upon the radiation belts, and relativistic electron microbursts. Future additions to the receiver network will increase the science potential and provide global coverage of space weather event signatures.
Mirco Marchetti - One of the best experts on this subject based on the ideXlab platform.
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making byzantine fault tolerant systems tolerate byzantine faults
Networked Systems Design and Implementation, 2009Co-Authors: Allen Clement, Lorenzo Alvisi, Mike Dahlin, Edmund L Wong, Mirco MarchettiAbstract:This paper argues for a new approach to building Byzantine fault tolerant replication systems. We observe that although recently developed BFT state machine replication protocols are quite fast, they don't tolerate Byzantine faults very well: a single faulty client or server is capable of rendering PBFT, Q/U, HQ, and Zyzzyva virtually unusable. In this paper, we (1) demonstrate that existing protocols are dangerously fragile, (2) define a set of principles for constructing BFT services that remain useful even when Byzantine faults occur, and (3) apply these principles to construct a new protocol, Aardvark. Aardvark can achieve peak performance within 40% of that of the best existing protocol in our tests and provide a significant fraction of that performance when up to f servers and any number of clients are faulty. We observe useful throughputs between 11706 and 38667 requests per second for a broad range of injected faults.
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Making Byzantine Fault Tolerant Systems Tolerate Byzantine Faults
2009Co-Authors: Allen Clement, Mirco Marchetti, Edmund Wong, Lorenzo Alvisi, Mike DahlinAbstract:Abstract: This paper is motivated by a simple observation: although recently developed BFT state machine replication protocols are quite fast, they don’t actually tolerate Byznatine faults very well. In particular a single faulty client or server in PBFT, Q/U, HQ, and Zyzzyva can render each of these systems effectively unusable for many applications by reducing their throughput by two orders of magnitude or more, from thousands of requests per second to fewer than 10 requests per second. The problem comes not because these systems fail to meet the guarantees they promise, but because the guarantees they promise are insufficient for the high assurance systems for which BFT techniques are likely to be of most interest. In this paper, we describe Aardvark, a new BFT replication protocol that guarantees good performance during uncivil periods, when the network is reliable but when up to f servers and any number of clients are faulty. Aardvark gives up some performance compared to protocols that focus on optimizing for the best case, but Aardvark’s peak throughput of 40527 requests per second seems sufficient for many applications. Because Aardvark is less aggressively tuned for the fault free case, it is guaranteed to remain within a constant factor of 40527 when faults occur. We observe throughputs of between 11706and 40527for a broad range of injected faults.
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Making Byzantine Fault Tolerant Systems Tolerate Byzantine Faults
2009Co-Authors: Lorenzo Alvisi, Allen Clement, Mirco Marchetti, Mike Dahlin, Edmund WongAbstract:This paper argues for a new approach to building Byzantine fault tolerant systems. We observe that although recently developed BFT state machine replication protocols are quite fast, they don’t actually tolerate Byzantine faults very well: a single faulty client or server is capable of rendering PBFT, Q/U, HQ, and Zyzzyva virtually unusable. In this paper, we (1) demonstrate that existing protocols are dangerously fragile, (2) define a set of principles for constructing BFT services that remain useful even when Byzantine faults occur, and (3) apply these new principles to construct a new protocol, Aardvark, which can achieve peak performance within 25 % of that of the best existing protocol in our tests and which provides a significant fraction of that performance when the network is well behaved and up to f servers and any number of clients are faulty. We observe useful throughputs between 11706 and 38667 for a broad range of injected faults
