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Various key-value (KV) stores are widely employed for data management to support Internet services as they offer higher efficiency, scalability, and availability than relational database systems. The log-structured merge tree (LSM-tree) based KV stores have attracted growing attention because they can eliminate random writes and maintain acceptable read performance. Recently, as the price per unit capacity of NAND flash decreases, solid state disks (SSDs) have been extensively adopted in enterprise-scale data centers to provide high I/O bandwidth and low access latency. However, it is inefficient to naively combine LSM-tree-based KV stores with SSDs, as the high parallelism enabled within the SSD cannot be fully exploited. Current LSM-tree-based KV stores are designed without assuming SSD's multi-channel architecture.To address this inadequacy, we propose LOCS, a system equipped with a customized SSD design, which exposes its internal flash channels to applications, to work with the LSM-tree-based KV store, specifically LevelDB in this work. We extend LevelDB to explicitly leverage the multiple channels of an SSD to exploit its abundant parallelism. In * This work was done during their visiting professorship at the Center for Energy-Efficient Computing and Applications in Peking University.† Jason Cong is also a co-director of the PKU/UCLA Joint Research Institute in Science and Engineering.Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. addition, we optimize scheduling and dispatching polices for concurrent I/O requests to further improve the efficiency of data access. Compared with the scenario where a stock LevelDB runs on a conventional SSD, the throughput of storage system can be improved by more than 4× after applying all proposed optimization techniques.

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Increasing the performances of SOFC is many-fold: i/ at low currentdensity, through the enhancement of the catalytic properties of theelectrodes, ii/ in the ohmic loss region, through lower resistance, iii/ inthe high current density region, via the optimization of the electrodesmicrostructure. The present work proposes to explore how thecorrugation of electrode/electrolyte interfaces impacts the performancesof SOFCs. Taking ideas from the battery community, this approach wasapplied to the anode/electrolyte interface of a SOFC based on standardcompositions. Patterning of this interface was achieved with differentgeometries at the 10-100 μm mesoscopic scale by cold pressing. Thinelectrolyte layers have been deposited on top of these architectures bydifferent techniques. In parallel, an electrochemical model was carriedout and implemented throughout the interface in finite element method(FEM) with COMSOL Multiphysics. The results showed a 25% increase in the total current density for a certain ellipsoid geometry.