Multi-level Caching in Distributed File Systems

We are investigating the potential for intermediate file servers to address scaling problems in increasingly large distributed file systems. To this end, we have run trace-driven simulations based on data from DEC-SRC and our own data collection to determine the potential of caching-only intermediate servers. The degree of sharing among clients is central to the effectiveness of an intermediate server. This turns out to be quite low in the traces available to us. All told, fewer than 10% of block accesses are to files shared by more than one file system client. Trace-driven simulation shows that even with an infinite cache at the intermediate, cache hit rates are disappointingly low. For client caches as small as 20 MB, we observe hit rates less than 19%. As client cache sizes increase, the hit rate at the intermediate approaches the degree of sharing among all clients. On the other hand, the intermediate does appear to be effective in reducing the peak load presented to upstream file servers.http://deepblue.lib.umich.edu/bitstream/2027.42/107967/1/citi-tr-91-3.pd

Does nitrate deposition following astrophysical ionizing radiation events pose an additional threat to amphibians?

It is known that amphibians are especially susceptible to the combination of heightened UVB radiation and increased nitrate concentrations. Various astrophysical events have been suggested as sources of ionizing radiation that could pose a threat to life on Earth, through destruction of the ozone layer and subsequent increase in UVB, followed by deposition of nitrate. In this study, we investigate whether the nitrate deposition following an ionizing event is sufficiently large to cause an additional stress beyond that of the heightened UVB previously considered. We have converted predicted nitrate depositions to concentration values, utilizing data from the New York State Department of Environmental Conservation Acid Rain Monitoring Network web site. Our results show that the increase in nitrate concentration in bodies of water following the most intense ionization event likely in the last billion years would not be sufficient to cause a serious additional stress on amphibian populations and may actually provide some benefit by acting as fertilizer.Comment: This version is a longer, more detailed draft of an article submitted to the journal Astrobiolog

Sow and Litter Performance for Two Genotypes in Crated and Group Gestation Systems

The effects of swine gestation housing on sow and litter performance of two genotypes were evaluated at the Iowa State University Lauren Christian Swine Research and Demonstration Farm near Atlantic, IA. The gestation housing systems were 1) individual gestation crates in a mechanically ventilated, manure flush confinement building with a partially slatted floor (CRATE); 2) group pens in a naturally ventilated, curtain-sided, modified-open front building with a partially slatted floor, no bedding and a deep manure pit (MOF); and 3) group pens in deepbedded, naturally ventilated hoop structures (HOOP). The group-housed gilts were individually fed with either individual feed stalls (FS) or computerized electronic feeders (EF). Sows fed with the electronic feeders were given an initial training period the week after breeding during which time they learned to use the feeders. The two sow genotypes were Yorkshire x Landrace (WHITE sows) and 1/4 Hampshire x 1/2 Yorkshire x 1/4 Landrace (COLOR sows). The Yorkshire and Landrace breeding was similar in both genotypes. Duroc terminal boars were mated to all sows. Farrowing occurred weekly throughout the year. Cross fostering occurred across all sows

Two Year Summary of the Performance of Finishing Pigs in Hoop Structures and Confinement during Winter and Summer

The objectives of the study were to document the performance of finishing pigs in hoops during the summer and winter, and to evaluate pig performance in hoops compared with pigs in a confinement housing system

Iowa’s Changing Swine Industry

Iowa has led the U.S. in swine production and pig inventory since the 1880s. Pig production has been a reliable value-added enterprise on many Iowa farms for generations. In spite of this 120-year national leadership, Iowa’s swine industry has been changing profoundly within the state

A Brownian-pumping model for oceanic trace metal scavenging: Evidence from Th isotopes

Two observed characteristics of Th isotope and stable metal sorption in natural aquatic systems are seemingly at odds with physico-chemical adsorption theory: (1) characteristic sorption times of days to weeks and (2) Kds which are inversely related in magnitude to particle concentrations. In addition, sorption rate constants are positiveiy correlated with particle concentrations and Kd. This paper presents a conceptual and mathematical model with which it is proposed that these metal sorption characteristics have the same underlying physical process in common: the coagulation of colloidal (nonfilterable) particles onto larger (filterable) particles. “Brownian pumping” (the transfer of truly dissolved metal species to filterable particles through a colloidal intermediate) consists of two rate steps: (1) rapid formation of metal/colloid surface site complexes (adsorption) and (2) slow coagulation of colloids with filterable particles. The Brownian-pumping model is tested against field and laboratory data. The field data, obtained from the literature, covers different regions of the oceans: deep ocean environments, euphotic zone, coastal and estuarine systems. The laboratory data involved 228Th sorption in suspensions of goethite and polystyrene latexes. Although the model has general applicability, results and discussions herein emphasize thorium isotope behavior. The Brownian-pumping model suggests that Th or other strongly sorbing elements may be useful as in situ “coagulometers” either at relatively high (e.g., greater than 5–10 mg/l) particle concentrations or when the mass ratio of colloids (C*p) to filterable particles (Cp) is known. The model also indicates that the ratio of colloids to filterable particles in marine systems, may be, by a first approximation, described by the relationship log C*p = 0.7 log Cp – 2.6 (in units of kg/l)