DDUC:an erasure-coded system with decoupled data updating and coding

In distributed storage systems,replication and erasure code(EC)are common methods for data redundancy.Compared with replication,EC has better storage efficiency,but suffers higher overhead in update.Moreover,consistency and reliability problems caused by concurrent updates bring new challenges to applications of EC.Many works focus on optimizing the EC solution,including algorithm optimization,novel data update method,and so on,but lack the solutions for consistency and reliability problems.In this paper,we introduce a storage system that decouples data updating and EC encoding,namely,decoupled data updating and coding(DDUC),and propose a data placement policy that combines replication and parity blocks.For the(N,M)EC system,the data are placed as N groups of M+1 replicas,and redundant data blocks of the same stripe are placed in the parity nodes,so that the parity nodes can autonomously perform local EC encoding.Based on the above policy,a two-phase data update method is implemented in which data are updated in replica mode in phase 1,and the EC encoding is done independently by parity nodes in phase 2.This solves the problem of data reliability degradation caused by concurrent updates while ensuring high concurrency performance.It also uses persistent memory(PMem)hardware features of the byte addressing and eight-byte atomic write to implement a lightweight logging mechanism that improves performance while ensuring data consistency.Experimental results show that the concurrent access performance of the proposed storage system is 1.70–3.73 times that of the state-of-the-art storage system Ceph,and the latency is only 3.4%–5.9%that of Ceph.

MXenes and MXene-based composites for energy conversion and storage applications

MXenes have received extensive attention from scholars due to their unique layered structure,significant electrical conductivity,and excellent mechanical properties.In addition to their pristine forms,they could also be incorporated with other components for attaining hybrids and nanocomposites,accompanying with amplified functionalities.It has been widely used in lithium batteries,supercapacitors,electromagnetic shielding,tumor therapy,biosensors,photocatalysis,and other fields,and has shown great application potential in energy conversion and storage.The purpose of this article is to encyclopaedically overview the latest progress in synthesis and characterization of MXenes,while their potential applications in energy conversation such as water splitting and solar cells,as well as in energy storage such as Li-ion batteries,supercapacitors,and hydrogen energy will be comprehensively elaborated.Development opportunities and challenges are summarized.

Chemical Bath Co-deposited ZnS Film Prepared from Different Zinc Salts: ZnSO_4—Zn(CH_3COO)_2, Zn(NO_3)_2—Zn(CH_3COO)_2,or ZnSO_4—Zn(NO_3)_2

ZnSO4-Zn（CH3COO）2, Zn（NO3）2-Zn（CH3COO）2, ZnSO4-Zn（NO3）2, ZnSO4, Zn（NO3）2 or Zn（CH3COO）2 have been used as zinc sources to prepare ZnS thin films by chemical bath deposition and co-deposition methods. Zn（NO3）2 or/and Zn（CH3COO）2 is/are favorable for cluster by cluster deposition process while ZnSO4 favors ion by ion deposition process regardless of concentration ratios of ZnSO4. However, Zn（NO3）2 affects the nucleation density of ZnS nuclei on the substrate. ZnS thin films deposited from ZnSO4-Zn（CH3COO）2 are not only more homogeneous and compact, but also have higher growth rate and adhesion on to the glass substrate. The cubic ZnS films are obtained after only single deposition. The average transmission of films from S6, S7, S8, S9 and S1 for 2 and 2.5 h is greater than 85% in visible region. Compared with the film from S6 （112 nm）, the film from S7 is not only thicker （125 nm）, but also more transparent. The band gaps of the films deposited from S6,S7, S8, S9 and S1 for 2 and 2.5 h range from 3.88 to 3.98 eV. The effects of anions from different zinc salts are discussed in detail.