Non-homogeneous Two-Rack Model for Distributed Storage Systems

In the traditional two-rack distributed storage system (DSS) model, due to the assumption that the storage capacity of each node is the same, the minimum bandwidth regenerating (MBR) point becomes infeasible. In this paper, we design a new non-homogeneous two-rack model by proposing a generalization of the threshold function used to compute the tradeoff curve. We prove that by having the nodes in the rack with higher regenerating bandwidth stores more information, all the points on the tradeoff curve, including the MBR point, become feasible. Finally, we show how the non-homogeneous two-rack model outperforms the traditional model in the tradeoff curve between the storage per node and the repair bandwidth.Comment: ISIT 2013. arXiv admin note: text overlap with arXiv:1004.0785 by other author

Cheilanthoid Ferns (Pteridaceae: Cheilanthoideae) in the Southwestern United States and Adjacent Mexico-A Molecular Phylogenetic Reassessment of Generic Lines

Cheilanthoids are the most commonly encountered fern species of the arid southwest and other xeric habitats throughout the world. Cheilanthes, Notholaena, Pellaea, and Bommeria are the best known southwestern genera, but some authors recognize segregate genera such as Argyrochosma, Aspidotis, Astrolepis, and Pentagramma. Others reject distinctions among some of these genera as artificial, leaving cheilanthoid generic concepts in a state of flux. This unsettled taxonomy is often attributed to morphological homoplasy associated with adaptation to xeric habitats, suggesting the need for new analyses that do not depend on potentially misleading morphology. Nucleotide sequences of the maternally inherited, chloroplast-encoded rbcL gene from 57 species that bear on the relationships of the cheilanthoids of the southwest were cladistically analyzed under the optimality criterion of maximum parsimony. The results provide new insights into phylogenetic relationships and generic circumscriptions of these ferns. Mexican Llavea cordifolia is rejected from the cheilanthoids, traditional Cheilanthes, Notholaena, and Pellaea are polyphyletic, and the segregations of Argyrochosma, Aspidotis, Astrolepis, and Pentagramma are supported. To assess confidence in these conclusions, results of the rbcL-based analysis are compared with those based on ITS sequences of biparentally inherited nuclear ribosomal DNA (nrDNA) for a subset of cheilanthoid taxa. These two data sets yield remarkably congruent topologies at shallower phylogenetic levels, suggesting that previous taxonomic problems in this group may indeed be attributable to difficulties in interpreting the taxonomic significance of morphological characters. Disagreement at deeper levels of the topologies suggests the need to incorporate data from less rapidly evolving nrDNA regions

The effects of molecular composition on thermal, electrochemical, and mechanical properties of hyperbranched polymer electrolytes

This dissertation examines how changing the hyperbranching density and structure of polymer host backbones affects the physical properties of solid state polymer electrolytes. The structure of interest in this dissertation is the hyperbranching polymer backbone, which includes tetrabranching and tribranching architectures of varying hyperbranching densities. For a series of poly(ethylene glycol)-based polymers, we consider how molecular architecture impacts the electrochemical, thermal, and mechanical properties of the electrolytes on both the bulk and macromolecular scales. For both architectures, decreasing hyperbranching densities lead to improved conductivities (tetra- at 9.45 • 10-4 S/cm and tri- at 1.95 • 10-3 S/cm at 80 ºC) and improved shear storage moduli (tetra- at 0.63 MPa and tri- at 1.24 at 90 ºC). While having superior ionic conductivity and shear strength, the tribranching electrolytes were not compatible with lithium, which is a necessity for lithium-ion battery application. Following successful synthesis and material characterization, the tetrabranching electrolytes of various hyperbranching densities and structures are further probed as electrolytes in lithium-ion batteries. This series showed improved cycling performance with decreasing hyperbranching density (specific capacity of 1175 mAh/gSi after 50 cycles), with improved energy storage capabilities relative to the liquid control electrolyte (763 mAh/gSi after 50 cycles). Ultimately, the solid state polymer electrolytes synthesized in this work are promising candidates for further use in energy storage devices due to their observed thermal, electrochemical, and mechanical stabilities

Molecular Species Identification with Rich Floristic Sampling: DNA Barcoding the Pteridophyte Flora of Japan

BACKGROUND: DNA barcoding is expected to be an effective identification tool for organisms with heteromorphic generations such as pteridophytes, which possess a morphologically simple gametophyte generation. Although a reference data set including complete coverage of the target local flora/fauna is necessary for accurate identification, DNA barcode studies including such rich taxonomic sampling on a countrywide scale are lacking. METHODOLOGY/PRINCIPAL FINDINGS: The Japanese pteridophyte flora (733 taxa including subspecies and varieties) was used to test the utility of two plastid DNA barcode regions (rbcL and trnH-psbA) with the intention of developing an identification system for native gametophytes. DNA sequences were obtained from each of 689 (94.0%) taxa for rbcL and 617 (84.2%) taxa for trnH-psbA. Mean interspecific divergence values across all taxon pairs (K2P genetic distances) did not reveal a significant difference in rate between trnH-psbA and rbcL, but mean K2P distances of each genus showed significant heterogeneity according to systematic position. The minimum fail rate of taxon discrimination in an identification test using BLAST (12.52%) was obtained when rbcL and trnH-psbA were combined, and became lower in datasets excluding infraspecific taxa or apogamous taxa, or including sexual diploids only. CONCLUSIONS/SIGNIFICANCE: This study demonstrates the overall effectiveness of DNA barcodes for species identification in the Japanese pteridophyte flora. Although this flora is characterized by a high occurrence of apogamous taxa that pose a serious challenge to identification using DNA barcodes, such taxa are limited to a small number of genera, and only minimally detract from the overall success rate. In the case that a query sequence is matched to a known apogamous genus, routine species identification may not be possible. Otherwise, DNA barcoding is a practical tool for identification of most Japanese pteridophytes, and is especially anticipated to be helpful for identification of non-hybridizing gametophytes

The evolution of the plastid chromosome in land plants: gene content, gene order, gene function

This review bridges functional and evolutionary aspects of plastid chromosome architecture in land plants and their putative ancestors. We provide an overview on the structure and composition of the plastid genome of land plants as well as the functions of its genes in an explicit phylogenetic and evolutionary context. We will discuss the architecture of land plant plastid chromosomes, including gene content and synteny across land plants. Moreover, we will explore the functions and roles of plastid encoded genes in metabolism and their evolutionary importance regarding gene retention and conservation. We suggest that the slow mode at which the plastome typically evolves is likely to be influenced by a combination of different molecular mechanisms. These include the organization of plastid genes in operons, the usually uniparental mode of plastid inheritance, the activity of highly effective repair mechanisms as well as the rarity of plastid fusion. Nevertheless, structurally rearranged plastomes can be found in several unrelated lineages (e.g. ferns, Pinaceae, multiple angiosperm families). Rearrangements and gene losses seem to correlate with an unusual mode of plastid transmission, abundance of repeats, or a heterotrophic lifestyle (parasites or myco-heterotrophs). While only a few functional gene gains and more frequent gene losses have been inferred for land plants, the plastid Ndh complex is one example of multiple independent gene losses and will be discussed in detail. Patterns of ndh-gene loss and functional analyses indicate that these losses are usually found in plant groups with a certain degree of heterotrophy, might rendering plastid encoded Ndh1 subunits dispensable

The Deletion of Vittaria graminifolia from the Flora of Florida

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