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

Evaluating Delayed Write in a Multilevel Caching File System

Delayed write in a multilevel file system cache hierarchy offers a way to improve performance in diverse client/server scenarios, such as integrating mass store into a distributed file system or providing distributed file system access over low-speed links. Using file system traces and cache simulations, we explore extensions and modifications to the traditional client caching model employed in such file systems as AFS, Sprite, and DFS. High cache hit rates at an intermediate cache server—a machine logically interposed between clients and servers that provides cached file service to the clients—combined with high client cache hit rates lend practicality to an integrated mass storage file system. In such a system, magnetic tape or optical-based mass storage devices may be used as a first-class data repository, fronted by disk and RAM caches to offer acceptable access times to the large, but slow, mass storage system. Similarly, a high cache hit rate is necessary for users accessing file systems via low-speed links, where a delayed write intermediate caching server can mediate traffic to make better use of available bandwidth. In an example taken from mobile computing, an intermediate server might be used as a docking station at a user's home. This arrangement would be convenient for users of mobile computers who upload large amounts of data generated while operating in disconnected mode. Simulations of delayed write caching strategies are applicable to both the mass storage and low-speed link scenarios.http://deepblue.lib.umich.edu/bitstream/2027.42/107940/1/citi-tr-95-9.pd

Comparison of steer behavior when housed in a deep-bedded hoop barn versus an open feedlot with shelter

The use of hoop barns as an alternative housing system for beef cattle has not been widely researched. The objectives of this study were to determine the main effects of behavior of steers 1) over winter and summer, 2) when housed in either a hoop barn or a conventional feedlot, and 3) interactions between season and housing system. A total of 960 crossbredBos taurus steers were used [August 2006 to April 2008 (2 winter and 2 summer trials)]. Steers were housed in either 1 deep-bedded hoop barn (n = 12 pens; 4.65 m2/steer) or 1 open feedlot with shelter (n = 12 pens; 14.7 m2/steer). Steers were ear tagged, implanted, and weighed (414 ± 36 kg) on arrival and allotted to treatments that were balanced for source, BW, and hide color. Behavioral data (3 postures and 2 behaviors) were collected using a 10-min live scan. The experimental unit for behavior was a pen of steers. Behavioral data were arcsine transformed to achieve a normal distribution. There were no (P \u3e 0.05) differences for time spent at bunk or waterer for steers between housing treatments. Steers housed in an open feedlot with shelter spent less time lying and more time standing and walking (P \u3c 0.05) compared with steers housed in a hoop barn. There were no (P = 0.32) differences between seasons for standing. Steers spent more time at the bunk (P \u3c 0.0001) and waterer (P \u3c 0.0001) in the summer compared with the winter. In the winter, steers engaged in more lying (P = 0.0002) and walking (P \u3c 0.0001). Overall, steers stood less (P = 0.006) and spent more time lying (P = 0.024) when housed in a hoop barn than in the open feedlot with shelter regardless of season. Steers housed in the open feedlot with shelter walked more (P \u3c 0.0001) than steers housed in the hoop barn and walked more (P \u3c 0.0001) in winter than in summer months (6 vs. 3%). There were no (P \u3e 0.05) differences in time spent at bunk and waterer between housing systems within season, but time spent at the waterer and bunk decreased (P \u3c 0.05) for both housing systems during the winter. In conclusion, housing 40 steers per pen in a cornstalk-bedded hoop barn at 4.65m2/steer does not result in adverse behavioral alterations and can be considered as a housing alternative for finishing steers in the Midwestern United States when compared with steers fed in an open feedlot with shelter provided

'Surely the most natural scenario in the world’: Representations of ‘Family’ in BBC Pre-school Television

Historically, the majority of work on British children’s television has adopted either an institutional or an audience focus, with the texts themselves often overlooked. This neglect has meant that questions of representation in British children’s television – including issues such as family, gender, class or ethnicity - have been infrequently analysed in the UK context. In this article, we adopt a primarily qualitative methodology and analyse the various textual manifestations of ‘family’, group, or community as represented in a selected number of BBC pre-school programmes. In doing so, we question the (limited amount of) international work that has examined representations of the family in children’s television, and argue that nuclear family structures do not predominate in this sphere

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