As computation continues to move into the cloud, the computing platform of interest no longer resembles a pizza box or a refrigerator, but a warehouse full of computers These new large datacenters are quite different from traditional hosting facilities of earlier times and cannot be viewed simply as a collection of co-located servers Large portions of the hardware and software resources in these facilities must work in concert to efficiently deliver good levels of Internet service performance, something that can only be achieved by a holistic approach to their design and deployment In other words, we must treat the datacenter itself as one massive warehouse-scale computer (WSC) We describe the architecture of WSCs, the main factors influencing their design, operation, and cost structure, and the characteristics of their software base We hope it will be useful to architects and programmers of today’s WSCs, as well as those of future many-core platforms which may one day implement the equivale

The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines, Second Edition

Parasitic dinoflagellates in the genus Hematodinium are important parasites of marine Crustacea. Outbreaks of these parasites have damaged commercial stocks of Norway lobster Nephrops norvegicus, snow crab Chionoecetes opilio, Tanner crab C. bairdi, American blue crab Callinectes sapidus, and velvet swimming crab Necora puber. Species of Hematodinium can reach high enough levels to regulate their host populations, but mortalities are also centred on the unfished juveniles and females, hosts not normally sampled by fisheries; hence impacts are often underre- ported. Seasonal prevalences of up to 85% occur annually in many host populations; in effect, these parasites form cryptic blooms in the water column with crabs and other crustaceans at risk of disease. We review the biology and ecology of Hematodinium spp. infections in crustaceans. Included is a comparison of the different infections, a synthesis of what is known, and an attempt to highlight fruitful areas for continued research.

/pdf/a-review-of-the-parasitic-dinoflagellates-hematodinium-3rp5nmg6an.pdf

A review of the parasitic dinoflagellates Hematodinium species and Hematodinium-like infections in marine crustaceans.

Online Social Networks (OSN) are fun, popular, and socially significant. An integral part of their success is the immense size of their global user base. To provide a consistent service to all users, Facebook, the world's largest OSN, is heavily dependent on centralized U.S. data centers, which renders service outside of the U.S. sluggish and wasteful of Internet bandwidth. In this paper, we investigate the detailed causes of these two problems and identify mitigation opportunities. Because details of Facebook's service remain proprietary, we treat the OSN as a black box and reverse engineer its operation from publicly available traces. We find that contrary to current wisdom, OSN state is amenable to partitioning and that its fine grained distribution and processing can significantly improve performance without loss in service consistency. Through simulations of reconstructed Facebook traffic over measured Internet paths, we show that user requests can be processed 79% faster and use 91% less bandwidth. We conclude that the partitioning of OSN state is an attractive scaling strategy for Facebook and other OSN services.

/pdf/exploiting-locality-of-interest-in-online-social-networks-28bann8c4v.pdf

Exploiting locality of interest in online social networks

In an attempt to develop a reproducible experimental model of bacterial infection in Crassostrea gigas, oysters taken from very localised sub-populations suffering natural mortality outbreaks were used in cohabitation trials under laboratory conditions. From these trials, a collection of Vibrio strains was isolated from moribund and healthy oysters. In a second step, strains were experimentally tested for virulence by means of injection into healthy oysters. This screening revealed a span of virulence among isolated strains from none to medium. When pooling injected strains, results suggest increased virulence. Vibrio strains may have additive/synergistic action leading to higher C. gigas mortality rates in experimental challenges. Although the study initially aimed to develop a simple experimental model, a complex of interactions emerged between several bacterial strains during the pathogenic process in their molluscan host. Selected strains provide a suitable model of experimental disease for further studies and better understanding of bacterial interaction and pathogenesis in C. gigas.

/pdf/screening-of-vibrio-isolates-to-develop-an-experimental-4g4ri1l8w6.pdf

Screening of Vibrio isolates to develop an experimental infection model in the Pacific oyster Crassostrea gigas.

http://digital.csic.es/bitstream/10261/25108/1/Acr67.tmp.pdf

Marteiliosis in molluscs: A review

Marteilia refringens is a major pathogen of the European flat oyster, Ostrea edulis Linnaeus. Since its description, the life-cycle of this protozoan parasite has eluded discovery. Attempts to infect oysters experimentally have been unsuccessful and led to the hypothesis of a complex life-cycle involving several hosts. Knowledge of this life-cycle is of central importance in order to manage oyster disease. However, the exploration of M. refringens life-cycle has been previously limited by the detection tools available and the tremendous number of species to be screened in enzootic areas. In this study, these two restrictions were circumvented by the use of both molecular detection tools and a mesocosm with low biodiversity. Screening of the entire fauna of the pond for M. refringens DNA was systematically undertaken using PCR. Here, we show that the copepod Paracartia (Acartia) grani is a host of M. refringens. Not only was DNA of M. refringens consistently detected in P. grani but also the presence of the parasite in the ovarian tissues was demonstrated using in situ hybridization. Finally, successful experimental transmissions provided evidence that P. grani can be infected from infected flat oysters.

/pdf/needle-in-a-haystack-involvement-of-the-copepod-paracartia-1vwuc0lu1k.pdf

Needle in a haystack: involvement of the copepod Paracartia grani in the life-cycle of the oyster pathogen Marteilia refringens

The protozoan parasite Marteilia refringens has been partly responsible for the severe decrease in the production of the European flat oyster Ostrea edulis Linnaeus in France since the 1970s. The calanoid copepod Paracartia grani Sars was recently found to be a host for M refringens in French shallow-water oyster ponds ('claires'). This study reconsidered M refringens transmission dynamics in the light of this finding, taking into account not only oyster infection dynamics and environmental factors but also data concerning the copepod host. P. grani population dynamics in the claire under study revealed that this species is the dominant planktonic copepod in this confined ecosystem. During winter, M refringens overwintered in O. edulis, with P. grani existing only as resting eggs in the sediment. The increase in temperature in spring controlled and synchronized both the release of M refringens sporangia in the oyster feces, and the hatching of the benthic resting eggs of the copepod. Infection of oysters by M refringens was limited to June, July and August, coinciding with (1) the highest temperature recorded in the claire, and (2) the highest abundance of P. grani. PCR detection of M refringens in P. grani during the summer period was linked to the release of parasite sporangia by the oyster. Our results are supported by previous results on the effective transmission of this parasite from the oyster to the copepod.

/pdf/infection-dynamics-of-marteilia-refringens-in-flat-oyster-52a69cv7ji.pdf

Benoit Sautour

Papers

Needle in a haystack: involvement of the copepod Paracartia grani in the life-cycle of the oyster pathogen Marteilia refringens

Infection dynamics of Marteilia refringens in flat oyster Ostrea edulis and copepod Paracartia grani in a claire pond of Marennes-Oléron Bay.