区域折射型多焦点人工晶状体植入术后视觉质量误差分析

目的:分析区域折射型多焦点人工晶状体植入术后客观视觉质量检查误差。方法:选取2019-01/2020-06在中山大学中山眼科中心海南眼科医院行白内障超声乳化摘除术的白内障患者116例180眼进行回顾性分析。根据植入人工晶状体类型,将患者分为两组,单焦组(61例96眼)植入Aspira-aA,多焦组(55例84眼)植入LS-313 MF30。术后3mo检查患者裸眼远视力(UCDVA)、最佳矫正远视力(BCDVA)、裸眼中视力(UCIVA)和裸眼近视力(UCNVA),采用Itrace视觉质量分析仪进行客观视觉质量检查,分析指标包括:全眼高阶像差(HOAt)、眼内高阶像差(HOAi)、角膜高阶像差(HOAc)、球差、彗差、三叶草差、斯特列尔比(SR)、调制传递函数平均高度(MTF AvgHeight)和晶状体失调指数(DLI)。结果:术后3mo,两组UCDVA及BCDVA比较无差异(t=-0.789、-0.815,均P>0.05);多焦组的UCIVA和UCNVA明显优于单焦组,比较均有差异(t=1.971、3.215,均P<0.05)。术后3mo,两组HOAc和球差的比较均无差异(t=1.126、-0.995,均P>0.05)。多焦组的HOAt、HOAi、彗差和三叶草差明显高于单焦组,比较均有差异(t=-2.518、-2.926、-2.859、-3.128,均P<0.05)。多焦组的SR、MTF AvgHeight和DLI明显低于单焦组,比较均有差异(t=2.8537、2.014、3.292,均P<0.05)。视网膜E字视标图、MTF和点扩散函数(PSF)曲线均显示,多焦组术后眼内和全眼像差显著增加,视网膜点阵(RSD)图显示,附加+3D球镜后,彗差和三叶草差明显增加。结论:区域折射型多焦点人工晶状体可以为患者提供优越的远中近视力,Itrace视觉质量分析仪对区域折射型多焦点人工晶状体植入术后像差测量分析可能存在误差,人工晶状体的设计本身可能会导致术后像差的增加和客观视觉质量的降低。

Analysis of Single-Walled Carbon Nanotubes Using a Chemical Bond Element Model

A three dimensional nano-scale finite element model （FEM）, called the chemical bond element model, is proposed for the simulation of mechanical properties of single-walled carbon nanotubes （SWCNTs） based upon molecular mechanics method. Chemical bonds between carbon atoms are modeled by chemical bond elements. The constants of a sub-stiffness matrix are determined by using a linkage between molecular mechanics and continuum mechanics. In order to evaluate the correctness and performance of the proposed model, simulation was done to determine the influence of nanotube wall thickness, radius and length on the elastic modulus （Young＇s modulus and shear modulus） of SWCNTs. The simulation results show that the choice of wall thickness significantly affects the Young＇s modulus and shear modulus. The force field constants is also very important, because the elastic modulus is sensitive to force field constants and the elastic properties of SWCNT are related to the radii of the tubes. The contribution of length to elastic modulus is insignificant and can be ignored. In comparison with the Young＇s modulus and shear modulus reported in the literature, the presented results agree very well with the corresponding theoretical results and many experimental measurements. Furthermore, if the force constants are properly chosen, the present method could be conveniently used to predict the mechanical behavior of other single-walled nanotubes such as boron nitride nanotubes. The results demonstrate the value of the proposed model as a valuable tool in the study of mechanical behaviors of carbon nanotubes and in the analysis of nanotube-based equipments.

A Modified Molecular Structural Mechanics Method for Analysis of Carbon Nanotubes

A modified molecular structural mechanics method, based on molecular mechanics and similar to the finite element method, was developed. The energy of a system was expressed by the force field functions of the molecular mechanics. Under the small deformation assumption and by the principle of minimum potential energy, the system function was established. The properties of tension and bending of single-walled carbon nanotubes were analyzed. The Young＇s modulus is about 0.36 TPa nm, which agrees perfectly with the results of previous analysis by other researchers. It is found, for the first time, that the Young＇s moduli, for Zigzag nanotubes, are different from each other when the system energy was expressed as the sum of two or three individual energy terms in molecular mechanics. Whereas, the Young＇s moduli were the same for the Armchair nanotubes. It is found, when simulating the bending, that the deflections are closer to the theoretical ones, of the classical elasticity, when the diameter of the carbon nanotube increases.

A wideband fast multipole boundary element method for half-space/plane-symmetric acoustic wave problems

This paper presents a novel wideband fast multipole boundary element approach to 3D half-space/planesymmetric acoustic wave problems.The half-space fundamental solution is employed in the boundary integral equations so that the tree structure required in the fast multipole algorithm is constructed for the boundary elements in the real domain only.Moreover,a set of symmetric relations between the multipole expansion coefficients of the real and image domains are derived,and the half-space fundamental solution is modified for the purpose of applying such relations to avoid calculating,translating and saving the multipole/local expansion coefficients of the image domain.The wideband adaptive multilevel fast multipole algorithm associated with the iterative solver GMRES is employed so that the present method is accurate and efficient for both lowand high-frequency acoustic wave problems.As for exterior acoustic problems,the Burton-Miller method is adopted to tackle the fictitious eigenfrequency problem involved in the conventional boundary integral equation method.Details on the implementation of the present method are described,and numerical examples are given to demonstrate its accuracy and efficiency.

Management Recommendations on Sleep Disturbance o Patients with Parkinson's Disease

INTRODUCTION Sleep disturbance is one of the most common nonmotor symptoms in Parkinson's disease (PD).Sleep disturbance affects 40-98% of PD patients in the world. In China, the prevalence of PD patients with sleep disturbance ranges from 47.66% to 89.10%. Sleep disturbance usually has adverse impact on the quality of life of PD patients. Apossible pathogenesis of PD with sleep disturbance include thalamocortical pathway degeneration and changes of neurotransmitter systems. The etiology of sleep disturbance is multifactorial,involving degeneration of areas regulating sleep,sleep structure affected by drugs,sleep disturbance induced by drug,and sleep fragmentation by multiple factors.

ShadowEth： Private Smart Contract on Public Blockchain

Blockchain is becoming popular as a distributed and reliable ledger which allows distrustful parties to transact safely without trusting third parties. Emerging blockchain systems like Ethereum support smart contracts where miners can run arbitrary user-defined programs. However, one of the biggest concerns about the blockchain and the smart contract is privacy, since all the transactions on the chain are exposed to the public. In this paper, we present ShadowEth, a system that leverages hardware enclave to ensure the confidentiality of smart contracts while keeping the integrity and availability based on existing public blockchains like Ethereum. ShadowEth establishes a confidential and secure platform protected by trusted execution environment （TEE） off the public blockchain for the execution and storage of private contracts. It only puts the process of verification on the blockchain. We provide a design of our system including a protocol of the cryptographic communication and verification and show the applicability and feasibility of ShadowEth by various case studies. We implement a prototype using the Intel SGX on the Ethereum network and analyze the security and availability of the system.

Unified Enclave Abstraction and Secure Enclave Migration on Heterogeneous Security Architectures

ion and secure enclave migration on heterogeneous security architectures.

Revisiting Persistent Indexing Structures on Intel Optane DCPersistent Memory

Persistent indexing structures are proposed in response to emerging non-volatile memory(NVM)to provide high performance yet durable indexes.However,due to the lack of real NVM hardware,many prior persistent indexing structures were evaluated via emulation,which varies a lot across different setups and differs from the real deployment.Recently,Intel has released its Optane DC Persistent Memory Module(PMM),which is the first production-ready NVM.In this paper,we revisit popular persistent indexing structures on PMM and conduct comprehensive evaluations to study the performance differences among persistent indexing structures,including persistent hash tables and persistent trees.According to the evaluation results,we find that Cacheline-Conscious Extendible Hashing(CCEH)achieves the best performance among all evaluated persistent hash tables,and Failure-Atomic ShifT B+-Tree(FAST)and Write Optimal Radix Tree(WORT)perform better than other trees.Besides,we find that the insertion performance of hash tables is heavily influenced by data locality,while the insertion latency of trees is dominated by the flush instructions.We also uncover that no existing emulation methods accurately simulate PMM for all the studied data structures.Finally,we provide three suggestions on how to fully utilize PMM for better performance,including using clflushopt/clwb with sfence instead of clflush,flushing continuous data in a batch,and avoiding data access immediately after it is flushed to PMM.

Preparation of Sm_2Fe_(17) alloy by reduction-diffusion process

SmFealloy is the intermediate material for the preparation of SmFeNx(x ≈ 3); thus, the synthesis of pure SmFemother alloy is the key to obtaining highperformance SmFeNx. Reduction-diffusion(R-D) is a cost-effective method. In this study, the R-D process of synthesizing SmFewas analyzed by scanning electron microscopy(SEM), energy-dispersive X-ray spectroscopy(EDX), X-ray diffraction(XRD), and X-ray fluorescence(XRF). Furthermore, the influences of the tightness of compacted reactants, the compensation amount of SmO,and the particle size of Fe on the formation of SmFewere discussed from the aspects of the three raw materials.The results show that Sm reduced from SmOreacts with Fe particles to form intermetallic compound SmFedirectly in the R-D reaction process of preparing SmFe;the generation of Sm and its migration to the surface of Fe particles control the reaction rate; a proper tightness of compacted reactants is necessary for ensuring the purity of SmFeproduct; pure SmFecan be obtained when the compensation of SmOis 33 % of the stoichiometry; and the sufficiency of the reaction improves with the decrease in the size of Fe powders under the same reaction condition.

SplitPass： A Mutually Distrusting Two-Party Password Manager

Using a password manager is known to be more convenient and secure than not using one, on the assmnption that the password manager itself is safe. However recent studies show that most popular password managers have security vulnerabilities that may be fooled to leak passwords without users＇ awareness. In this paper, we propose a new password manager, SplitPass, which vertically separates both the storage and access of passwords into two mutually distrusting parties. During login, all the parties will collaborate to send their password shares to the web server, but none of these parties will ever have the complete password, which significantly raises the bar of a successful attack to compromise all of tile parties. To retain transparency to existing applications and web servers, SplitPass seamlessly splits the secure sockets layer （SSL） and transport layer security （TCP） sessions to process on all parties, and makes the joining of two password shares transparent to the web servers. We have implemented SplitPass using an Android phone and a cloud assistant and evaluated it using 100 apps from top free apps in the Android official market. The evaluation shows that SplitPass securely protects users＇ passwords, while incurring little performance overhead and power consumption.

Scaling out NUMA-Aware Applications with RDMA-Based Distributed Shared Memory

The multicore evolution has stimulated renewed interests in scaling up applications on shared-memory multiprocessors,significantly improving the scalability of many applications.But the scalability is limited within a single node;therefore programmers still have to redesign applications to scale out over multiple nodes.This paper revisits the design and implementation of distributed shared memory (DSM)as a way to scale out applications optimized for non-uniform memory access (NUMA)architecture over a well-connected cluster.This paper presents MAGI,an efficient DSM system that provides a transparent shared address space with scalable performance on a cluster with fast network interfaces.MAGI is unique in that it presents a NUMA abstraction to fully harness the multicore resources in each node through hierarchical synchronization and memory management.MAGI also exploits the memory access patterns of big-data applications and leverages a set of optimizations for remote direct memory access (RDMA)to reduce the number of page faults and the cost of the coherence protocol.MAGI has been implemented as a user-space library with pthread-compatible interfaces and can run existing multithreaded applications with minimized modifications.We deployed MAGI over an 8-node RDMA-enabled cluster.Experimental evaluation shows that MAGI achieves up to 9.25:4 speedup compared with an unoptimized implementation,leading to a sealable performance for large-scale data-intensive applications.

Optimistic Transaction Processing in Deterministic Database

Deterministic databases can improve the performance of distributed workload by eliminating the distributed commit protocol and reducing the contention cost.Unfortunately,the current deterministic scheme does not consider the performance scalability within a single machine.In this paper,we describe a scalable deterministic concurrency control,Deterministic and Optimistic Concurrency Control(DOCC),which is able to scale the performance both within a single node and across multiple nodes.The performance improvement comes from enforcing the determinism lazily and avoiding read-only transaction blocking the execution.The evaluation shows that DOCC achieves 8x performance improvement than the popular deterministic database system,Calvin.

Mercury: Combining Performance with Dependability Using Self-Virtualization

Virtualization has recently gained popularity largely due to its promise in increasing utilization, improving availability and enhancing security. Very often, the role of computer systems needs to change as the business environment changes. Initially, the system may only need to host one operating system and seek full execution speed. Later, it may be required to add other functionalities such as allowing easy software/hardware maintenance, surviving system failures and hosting multiple operating systems. Virtualization allows these functionalities to be supported easily and effectively. However, virtualization techniques generally incur non-negligible performance penalty. Fortunately, many virtualization- enabled features such as online software/hardware maintenance and fault tolerance do not require virtualization standby all the time. Based on this observation, this paper proposes a technique, called Self-virtualization, which provides the operating system with the capability to turn on and off virtualization on demand, without disturbing running applications. This technique enables computer systems to reap most benefits from virtualization without sacrificing performance. This paper presents the design and implementation of Mercury, a working prototype based on Linux and Xen virtual machine monitor. The performance measurement shows that Mercury incurs very little overhead： about 0.2 ms on 3 GHz Xeon CPU to complete a mode switch, and negligible performance degradation compared to Linux.

Special Section of JCST on Computer Architecture and Systems with Emerging Technologies

Introduction Research on computer architecture and systems is typically driven by technology and applications. Emerging technologies, such as non-volatile memory, brain-inspired computing and quantum computing, are shaping the future of computing. However, it is still at its early stage to use these technologies to build computer systems. This special section is an effort to encourage and promote research on emerging technologies from the computer architecture and software perspective.