Signal Processing for Caching Networks and Non-volatile Memories

The recent information explosion has created a pressing need for faster and more reliable data storage and transmission schemes. This thesis focuses on two systems: caching networks and non-volatile storage systems. It proposes network protocols to improve the efficiency of information delivery and signal processing schemes to reduce errors at the physical layer as well. This thesis first investigates caching and delivery strategies for content delivery networks. Caching has been investigated as a useful technique to reduce the network burden by prefetching some contents during o˙-peak hours. Coded caching [1] proposed by Maddah-Ali and Niesen is the foundation of our algorithms and it has been shown to be a useful technique which can reduce peak traffic rates by encoding transmissions so that different users can extract different information from the same packet. Content delivery networks store information distributed across multiple servers, so as to balance the load and avoid unrecoverable losses in case of node or disk failures. On one hand, distributed storage limits the capability of combining content from different servers into a single message, causing performance losses in coded caching schemes. But, on the other hand, the inherent redundancy existing in distributed storage systems can be used to improve the performance of those schemes through parallelism. This thesis proposes a scheme combining distributed storage of the content in multiple servers and an efficient coded caching algorithm for delivery to the users. This scheme is shown to reduce the peak transmission rate below that of state-of-the-art algorithms

Spreading modulation for multi-level non-volatile memories

The aggressive scaling of NAND flash memories has caused significant degradation in their reliability and endurance. One of the dominant factors in this degradation is the intercell-interference, by which the programming of a cell can affect nearby neighboring cells corrupting the information that they store. This paper proposes a new data representation scheme, which increases endurance and significantly reduces the probability of error caused by inter-cell-interference. The method is based on using an orthogonal code to spread each bit across multiple cells, resulting in lower variance for the voltages being programmed in the cells. This new data representation method is also shown to present many of the advantages that spreading sequences bring to wireless communications. For example, multiple information sequences can be written on the same cells at different times without interfering with each other. It also allows storing additional information on an already programmed memory in such a way that the new information is hidden by the noise

Single crystal of a one-dimensional metallo-covalent organic framework.

Although polymers have been studied for well over a century, there are few examples of covalently linked polymer crystals synthesised directly from solution. One-dimensional (1D) covalent polymers that are packed into a framework structure can be viewed as a 1D covalent organic framework (COF), but making a single crystal of this has been elusive. Herein, by combining labile metal coordination and dynamic covalent chemistry, we discover a strategy to synthesise single-crystal metallo-COFs under solvothermal conditions. The single-crystal structure is rigorously solved using single-crystal electron diffraction technique. The non-centrosymmetric metallo-COF allows second harmonic generation. Due to the presence of syntactic pendant amine groups along the polymer chains, the metallopolymer crystal can be further cross-linked into a crystalline woven network

Coded Caching for Distributed Storage

Content delivery networks store information distributed across multiple servers, so as to balance the load and avoid unrecoverable losses in case of node or disk failures. Coded caching has been shown to be a useful technique which can reduce peak traffic rates by pre-fetching popular content at the end users and encoding transmissions so that different users can extract different information from the same packet. On one hand, distributed storage limits the capability of combining content from different servers into a single message, causing performance losses in coded caching schemes. But, on the other hand, the inherent redundancy existing in distributed storage systems can be used to improve the performance of those schemes through parallelism. This paper designs coded caching and delivery schemes tailored towards systems where the library is distributed across multiple servers, possibly with some redundancy in the form of maximum distance separable (MDS) erasure codes. Different schemes are proposed based on the capacity of the users' caches, as well as the number of parity servers. The main focus is on scenarios with one (RAID-4) or two (RAID-6) parity servers, but the paper also includes simple extensions for cases with more than two or no parity servers at all. The proposed schemes are shown to reduce the worst case latency, or equivalently the peak transmission rate from any server, below that of state-of-the-art algorithms

Research Status and Development Trend of Piezoelectric Accelerometer

Piezoelectric accelerometers have been widely used because of their large range, simple structure, stable performance, and other advantages. With the improvement of science and technology, the application field is expanding, but there are still some problems in high-temperature environments and low-frequency vibration conditions. Under high-temperature environments, the piezoelectric material will undergo depolarization or resistance change, resulting in sensor failure. Aerospace instruments, water conservancy platforms, and other fields require high-precision instruments with vibration amplitudes of the order of a few microns in the range of 0.01–1 Hz, which require low-frequency and ultra-low-frequency sensors for the measurements. Therefore, how to increase the operating temperature and reduce the noise of piezoelectric accelerometers has become a problem that needs to be solved. This paper reviews the structure, principle, application range, and material selection of piezoelectric components of different types of piezoelectric accelerometers and summarizes the current problems and future research priorities

"on Water" Direct Organocatalytic Cyanoarylmethylation of Isatins for the Diastereoselective Synthesis of 3-Hydroxy-3-cyanomethyl Oxindoles

An "on water" organocatalytic cyanoarylmethylation of aryl acetonitrile to isatins is developed, giving products in high yields and up to excellent diastereoselectivities. A remarkable enhancement of reaction rates and diastereoselectivities by water was observed under mild conditions. Moreover, this approach provides a highly efficient and environmentally benign access to thermodynamic 3-hydroxy-3-cyanomethyl oxindoles.Accepted Author ManuscriptChemE/Inorganic Systems Engineerin