15,375 research outputs found
Kink-induced transport and segregation in oscillated granular layers
We use experiments and molecular dynamics simulations of vertically
oscillated granular layers to study horizontal particle segregation induced by
a kink (a boundary between domains oscillating out of phase). Counter-rotating
convection rolls carry the larger particles in a bidisperse layer along the
granular surface to a kink, where they become trapped. The convection
originates from avalanches that occur inside the layer, along the interface
between solidified and fluidized grains. The position of a kink can be
controlled by modulation of the container frequency, making possible systematic
harvesting of the larger particles.Comment: 4 pages, 5 figures. to appear in Phys. Rev. Let
Additive Schwarz Preconditioners for a State Constrained Elliptic Distributed Optimal Control Problem Discretized by a Partition of Unity Method
The minimization problem (2) is discretized in [4] by a partition of unity method (PUM). The goal of this paper is to use the ideas in [5] for an obstacle problem of clamped Kirchhoff plates to develop preconditioners for the discrete problems in [4]
A partition of unity method for the displacement obstacle problem of clamped Kirchhoff plates
A partition of unity method for the displacement obstacle problem of clamped Kirchhoff plates is considered in this paper. We derive optimal error estimates and present numerical results that illustrate the performance of the method. © 2013 Elsevier B.V. All rights reserved
20 K superconductivity in heavily electron doped surface layer of FeSe bulk crystal
A superconducting transition temperature Tc as high as 100 K was recently
discovered in 1 monolayer (1ML) FeSe grown on SrTiO3 (STO). The discovery
immediately ignited efforts to identify the mechanism for the dramatically
enhanced Tc from its bulk value of 7 K. Currently, there are two main views on
the origin of the enhanced Tc; in the first view, the enhancement comes from an
interfacial effect while in the other it is from excess electrons with strong
correlation strength. The issue is controversial and there are evidences that
support each view. Finding the origin of the Tc enhancement could be the key to
achieving even higher Tc and to identifying the microscopic mechanism for the
superconductivity in iron-based materials. Here, we report the observation of
20 K superconductivity in the electron doped surface layer of FeSe. The
electronic state of the surface layer possesses all the key spectroscopic
aspects of the 1ML FeSe on STO. Without any interface effect, the surface layer
state is found to have a moderate Tc of 20 K with a smaller gap opening of 4
meV. Our results clearly show that excess electrons with strong correlation
strength alone cannot induce the maximum Tc, which in turn strongly suggests
need for an interfacial effect to reach the enhanced Tc found in 1ML FeSe/STO.Comment: 5 pages, 4 figure
Fast Reconstruction for Degraded Reads and Recovery Process in Primary Array Storage Systems
RAID has been widely deployed in disk array storage systems to manage both performance and reliability simultaneously. RAID conducts two performance-critical operations during disk failures known as degraded reads/writes and recovery process. Before the recovery process is complete, reads and writes are degraded because data is reconstructed using data redundancy. The performance of degraded reads/writes is critical in order to meet stipulations in customer service level agreements (SLAs), and the recovery process affects the reliability of a storage system considerably. Both operations require fast data reconstruction. Among the erasure codes for fast reconstruction, Local Reconstruction Codes (LRC) are known to offer the best (or optimal) trade-off between storage overhead, fault tolerance, and the number of disks involved in reconstruction. Originally, LRC was designed for fast reconstruction in distributed cloud storage systems, in which network traffic is a major bottleneck during reconstruction. Thus, LRC focuses on reducing the number of disks involved in data reconstruction, which reduces network traffic. However, we observe that when LRC is applied to primary array storage systems, a major bottleneck in reconstruction results from uneven disk utilization. In other words, underutilized disks can no longer receive I/O requests as a result of the bottleneck of overloaded disks. Uneven disk utilization in LRC is due to its dedicated group partitioning policy to achieve the Maximally Recoverable property. In this paper, we present Distributed Reconstruction Codes (DRC) that support fast reconstruction in primary array storage systems. DRC is designed with group shuffling policy to solve the problem of uneven disk utilization. Experiments on real-world workloads show that DRC using global parity rotation (DRC-G) improves degraded performance by as much as 72% compared to RAID-6 and by as much as 35% compared to LRC under the same reliability. In addition, our study shows that DRC-G reduces the recovery process completion time by as much as 52% compared to LRC.1100Ysciescopu
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