Rewriting Flash Memories by Message Passing

This paper constructs WOM codes that combine rewriting and error correction for mitigating the reliability and the endurance problems in flash memory. We consider a rewriting model that is of practical interest to flash applications where only the second write uses WOM codes. Our WOM code construction is based on binary erasure quantization with LDGM codes, where the rewriting uses message passing and has potential to share the efficient hardware implementations with LDPC codes in practice. We show that the coding scheme achieves the capacity of the rewriting model. Extensive simulations show that the rewriting performance of our scheme compares favorably with that of polar WOM code in the rate region where high rewriting success probability is desired. We further augment our coding schemes with error correction capability. By drawing a connection to the conjugate code pairs studied in the context of quantum error correction, we develop a general framework for constructing error-correction WOM codes. Under this framework, we give an explicit construction of WOM codes whose codewords are contained in BCH codes.Comment: Submitted to ISIT 201

Coset Coding to Extend the Lifetime of Non-Volatile Memory

<p>Modern computing systems are increasingly integrating both Phase Change Memory (PCM) and Flash memory technologies into computer systems being developed today, yet the lifetime of these technologies is limited by the number of times cells are written. Due to their limited lifetime, PCM and Flash may wear-out before other parts of the system. The objective of this dissertation is to increase the lifetime of memory locations composed of either PCM or Flash cells using coset coding. </p><p>For PCM, we extend memory lifetime by using coset coding to reduce the number of bit-flips per write compared to un-coded writes. Flash program/erase operation cycle degrades page lifetime; we extend the lifetime of Flash memory cells by using coset coding to re-program a page multiple times without erasing. We then show how coset coding can be integrated into Flash solid state drives.</p><p>We ran simulations to evaluate the effectiveness of using coset coding to extend PCM and Flash lifetime. We simulated writes to PCM and found that in our simulations coset coding can be used to increase PCM lifetime by up to 3x over writing un-coded data directly to the memory location. We extended the lifetime of Flash using coset coding to re-write pages without an intervening erase and were able to re-write a single Flash page using coset coding more times than when writing un-coded data or using prior coding work for the same area overhead. We also found in our simulations that using coset coding in a Flash SSD results in higher lifetime for a given area overhead compared to un-coded writes.</p>Dissertatio

저밀도 부호의 응용: 묶음 지그재그 파운틴 부호와 WOM 부호

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 노종선.This dissertation contains the following two contributions on the applications of sparse codes. Fountain codes Batched zigzag (BZ) fountain codes – Two-phase batched zigzag (TBZ) fountain codes Write-once memory (WOM) codes – WOM codes implemented by rate-compatible low-density generator matrix (RC-LDGM) codes First, two classes of fountain codes, called batched zigzag fountain codes and two-phase batched zigzag fountain codes, are proposed for the symbol erasure channel. At a cost of slightly lengthened code symbols, the involved message symbols in each batch of the proposed codes can be recovered by low complexity zigzag decoding algorithm. Thus, the proposed codes have low buffer occupancy during decoding process. These features are suitable for receivers with limited hardware resources in the broadcasting channel. A method to obtain degree distributions of code symbols for the proposed codes via ripple size evolution is also proposed by taking into account the released code symbols from the batches. It is shown that the proposed codes outperform Luby transform codes and zigzag decodable fountain codes with respect to intermediate recovery rate and coding overhead when message length is short, symbol erasure rate is low, and available buffer size is limited. In the second part of this dissertation, WOM codes constructed by sparse codes are presented. Recently, WOM codes are adopted to NAND flash-based solid-state drive (SSD) in order to extend the lifetime by reducing the number of erasure operations. Here, a new rewriting scheme for the SSD is proposed, which is implemented by multiple binary erasure quantization (BEQ) codes. The corresponding BEQ codes are constructed by RC-LDGM codes. Moreover, by putting RC-LDGM codes together with a page selection method, writing efficiency can be improved. It is verified via simulation that the SSD with proposed rewriting scheme outperforms the SSD without and with the conventional WOM codes for single level cell (SLC) and multi-level cell (MLC) flash memories.1 Introduction 1 1.1 Background 1 1.2 Overview of Dissertation 5 2 Sparse Codes 7 2.1 Linear Block Codes 7 2.2 LDPC Codes 9 2.3 Message Passing Decoder 11 3 New Fountain Codes with Improved Intermediate Recovery Based on Batched Zigzag Coding 13 3.1 Preliminaries 17 3.1.1 Definitions and Notation 17 3.1.2 LT Codes 18 3.1.3 Zigzag Decodable Codes 20 3.1.4 Bit-Level Overhead 22 3.2 New Fountain Codes Based on Batched Zigzag Coding 23 3.2.1 Construction of Shift Matrix 24 3.2.2 Encoding and Decoding of the Proposed BZ Fountain Codes 25 3.2.3 Storage and Computational Complexity 28 3.3 Degree Distribution of BZ Fountain Codes 31 3.3.1 Relation Between $\Psi(x)$ and $\Omega(x)$ 31 3.3.2 Derivation of $\Omega(x)$ via Ripple Size Evolution 32 3.4 Two-Phase Batched Zigzag Fountain Codes with Additional Memory 40 3.4.1 Code Construction 41 3.4.2 Bit-Level Overhead 46 3.5 Numerical Analysis 49 4 Write-Once Memory Codes Using Rate-Compatible LDGM Codes 60 4.1 Preliminaries 62 4.1.1 NAND Flash Memory 62 4.1.2 Rewriting Schemes for Flash Memory 62 4.1.3 Construction of Rewriting Codes by BEQ Codes 65 4.2 Proposed Rewriting Codes 67 4.2.1 System Model 67 4.2.2 Multi-rate Rewriting Codes 68 4.2.3 Page Selection for Rewriting 70 4.3 RC-LDGM Codes 74 4.4 Numerical Analysis 76 5 Conclusions 80 Bibliography 82 초록 94Docto

NASA Tech Briefs, July 1990

Topics include: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Semiannual review of research and advanced development, 1 January - 30 June 1969. Volume 2 - /OART/

Supporting research and technology on spacecraft propulsion and electronic system

The Fifth NASA Symposium on VLSI Design

The fifth annual NASA Symposium on VLSI Design had 13 sessions including Radiation Effects, Architectures, Mixed Signal, Design Techniques, Fault Testing, Synthesis, Signal Processing, and other Featured Presentations. The symposium provides insights into developments in VLSI and digital systems which can be used to increase data systems performance. The presentations share insights into next generation advances that will serve as a basis for future VLSI design

Understanding Quantum Technologies 2022

Understanding Quantum Technologies 2022 is a creative-commons ebook that provides a unique 360 degrees overview of quantum technologies from science and technology to geopolitical and societal issues. It covers quantum physics history, quantum physics 101, gate-based quantum computing, quantum computing engineering (including quantum error corrections and quantum computing energetics), quantum computing hardware (all qubit types, including quantum annealing and quantum simulation paradigms, history, science, research, implementation and vendors), quantum enabling technologies (cryogenics, control electronics, photonics, components fabs, raw materials), quantum computing algorithms, software development tools and use cases, unconventional computing (potential alternatives to quantum and classical computing), quantum telecommunications and cryptography, quantum sensing, quantum technologies around the world, quantum technologies societal impact and even quantum fake sciences. The main audience are computer science engineers, developers and IT specialists as well as quantum scientists and students who want to acquire a global view of how quantum technologies work, and particularly quantum computing. This version is an extensive update to the 2021 edition published in October 2021.Comment: 1132 pages, 920 figures, Letter forma

Designing Functional Materials Driven by the Lattice Degree of Freedom

Advanced functional materials play a vital role in modern industry and human society. Therefore, accelerating the discovery and exploration of novel functional materials is critical for us as a society to tackle energy issues and further developments. In this regard, computational materials science based on quantum mechanics is now well established as a crucial pillar in condensed matter physics, chemistry, and materials science research, in addition to experiments and phenomenological theories. In this thesis, the strategy of designing new functional materials driven by the lattice degree of freedom is explored, where "lattice" refers to (1) the ground state crystal structures, (2) elementary excitations as represented by phonons, (3) coupling within themselves (i.e., anharmonicity) and the other degrees of freedom (i.e., electron-phonon interaction). We systematically studied several classes of physical phenomena and the resulting properties, such as magneto-structural coupling and magnetocalorics, anharmonicity and thermal conductivity, electron-phonon interaction and superconductivity. Additionally, an integrated computational paradigm that combines high-throughput (HTP) calculations, phonon theory, and CALPHAD methods is established and applied to design metastable functional materials, extending the applicability of DFT beyond 0 K. Considering lattice as crystal structures, we selected MAB phases with nanolaminated crystal structure as a test case, and performed an HTP screening for stable magnetic MAB compounds and predicted potential candidate magnets for permanent magnets and magnetocaloric applications. After a comprehensive validation, 21 novel compounds are predicted to be stable based on the systematic evaluation of thermodynamic, mechanical, and dynamical stabilities, and the number of stable compounds is increased to 434 taking the tolerance of convex hull being 100 meV/atom. The detailed evaluation of the magnetocrystalline anisotropy energy (MAE) and the magnetic deformations leads to 23 compounds with significant uniaxial anisotropy (MAE > 0.4 MJ/m3) and 99 systems with reasonable magnetic deformation (> 1.5 %). For those compounds containing no expensive, toxic, or critical elements, it is observed that Fe3Zn2B2 is a reasonable candidate as gap permanent magnet, and Fe4AlB4, Fe3AlB4, Fe3ZnB4, and Fe5B2 as potential magnetocaloric materials. This work paves the way for designing novel magnetic materials for energy applications based on the combinatorial sampling of the chemical space with specific crystal structure prototypes. Moreover, considering the elementary excitations of lattice vibrations, i.e., phonons, the anharmonicity caused by phonon-phonon interaction leads to many intriguing properties, such as the lattice thermal conductivity. We performed DFT calculations to evaluate the thermal transport properties of novel 2D MoSi2N4 and WSi2N4, and found their thermal conductivities being 162 W/mK and 88 W/mK at room temperature, respectively, which are 7 and 4 times the one for monolayer MoS2, 16 and 9 times the one for silicone. These results show that, MoSi2N4 and WSi2N4 have promising potential being thermal management materials. Additionally, to gain insight into the low thermal conductivity of 2D materials, we investigated the mechanism of anharmonicity from the fundamental phonon mode and electronic structure level for GaX (X= N, P, As). The thermal conductivity of GaP is calculated to be 1.52 W/mK, which is unexpectedly ultra-low and in sharp contrast to GaN and GaAs. The reason for the low thermal conductivity of the GaP can be attributed to the fact that the FA phonon dominates the thermal conductivity of GaN but contributes less to that of GaP, which is due to the symmetry-based selection rule and difference in atomic structure. The phonon anharmonicity quantified by the Grüneisen parameter is further analyzed to understand the phonon–phonon scattering, indicating the strong phonon-phonon scattering of GaP and the strongest phonon anharmonicity of GaP. The buckling structure has a strong influence on the anharmonicity, leading to low thermal conductivity. The non-bonding lone pair electrons of P and As atoms are stronger, which induces nonlinear electrostatic forces upon thermal agitation, leading to increased phonon anharmonicity in the lattice and thus reducing the thermal conductivity. Furthermore, high order phonon anharmonicity could have a significant effect on the thermal transport properties in materials within strong anharmonicity. Hence, we calculated the thermal conductivity of pristine EuTiO3. And the role of the quartic anharmonicity in the lattice dynamics and thermal transport of the cubic EuTiO3 was elucidated by combining ab initio self-consistent phonon theory with compressive sensing techniques. The anti-ferromagnetic G-type magnetic structure is used to mimic the para-magnetic EuTiO3. We find that the strong quartic anharmonicity of oxygen atoms plays an important role in the phonon quasiparticles without imaginary frequencies and causes the hardening of the vibrational frequencies of soft modes. Furthermore, in terms of electron-phonon interaction, we derived from DFT calculations the formation energies of a newly synthesized orthorhombic compound GeNCr3, which is a metastable phase. In accordance with the experimentally discovered superconductivity in antiperovskite MgCNi3, we performed calculations to evaluate the electron-phonon interaction and the resulting superconducting critical temperature of GeNCr3. It is observed that its superconducting temperature is about 8.2 K, driven by the electron-phonon interaction. Correspondingly, it is suspected that superconductivity may exist in the other MAX, MAB, and APV compounds, which will be investigated in the future based on the established workflow to evaluate the electron-phonon coupling. Such a workflow allows us to obtain the T-dependence of electric conductivities and also the lattice thermal conductivities. Last but not least, considering the thermodynamic properties where the lattice free energy plays a dominant role at the finite temperatures, we combined DFT calculations and CALPHAD modeling to optimize the phase diagrams, which can be validated with experiments and be bridged to phase field simulations to map out the processing-microstructure-property relationships. For instance, the thermodynamic properties of the Fe-Sn system are studied. First-principles phonon calculations with the quasi-harmonic approximation (QHA) approach were performed to compute the thermodynamic properties at finite temperatures. Thermodynamic properties, phonon dispersions of pure elements, and intermetallics were predicted to make up for the shortage of experimental data. A set of self-consistent thermodynamic parameters of the Fe-Sn system are obtained by the CALPHAD approach. Thermodynamic modeling of the Fe-Sn phase diagram has been re-established. The metastable phase Fe3Sn was first introduced into the current metastable phase diagram and corrected phase locations of Fe5Sn3 and Fe3Sn2 under the newly measured corrected temperature ranges. In summary, in my thesis, a systematic computational paradigm has been established based on DFT to tackle both the thermodynamic and non-equilibrium transport properties associated with the lattice degree of freedom. Such a paradigm allows us to design and optimize functional materials with physical properties driven by magneto-structural coupling, phonon-phonon coupling, and electron-phonon interaction, and also to bridge to large-scale simulations

2021-2022 University of Nebraska at Omaha Catalog

Located in one of America’s best cities to live, work and learn, the University of Nebraska at Omaha (UNO) is Nebraska’s premier metropolitan university. With more than 15,000 students enrolled in 200-plus programs of study, UNO is recognized nationally for its online education, graduate education, military friendliness, and community engagement efforts. Founded in 1908, UNO has served learners of all backgrounds for more than 100 years and is dedicated to another century of excellence both in the classroom and in the communit

Review of Particle Physics

The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances. The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings