Blockchain-based query with its traceability and data provenance has become increasingly popular and widely adopted in numerous applications. Yet existing index-based query approaches are only efficient under static blockchain query workloads where the query attribute or type must be fixed. It turns out to be particularly challenging to construct an efficient index for dynamic workloads due to prohibitively long construction time and excessive storage consumption. In this paper, we present FlexIM, the first efficient and verifiable index management system for blockchain dynamic queries. The key innovation in FlexIM is to uncover the inherent characteristics of blockchain, i.e., data distribution and block access frequency, and then to optimally choose the index by utilizing reinforcement learning technique under varying workloads. In addition, we enhance and facilitate verifiability with low storage overhead by leveraging Root Merkle Tree (RMT) and Bloom Filter Merkle Tree (BMT). Our comprehensive evaluations demonstrate that FlexIM outperforms the state-of-the-art blockchain query mechanism, vChain+, by achieving a 26.5% speedup while consuming 94.2% less storage, on average, over real-world Bitcoin datasets.

The privacy-preserving query is critical for modern blockchain systems, especially when supporting many crucial applications such as finance and healthcare. Recent advances in blockchain query schemes mainly focus on enhancing the traceability efficiency of integrity authentication. Despite these efforts, we argue that the exposure of retrieval information may result in privacy leakage, which inevitably poses an important yet unresolved challenge. In this paper, we introduce Cloak, a novel privacy-preserving blockchain query scheme with two notable features. First, it utilizes a two-phase distributed query requests technique, i.e., division and aggregation, to hide retrieval information based on the natural independent characteristic of blockchain. Second, we add noise to the sub-request set to avoid malicious attacks during transmission and adopt smart contract-based asymmetric encryption to guarantee the correctness of query results. Experimental results demonstrate that Cloak improves the query performance by up to 4× and reduces the storage overhead by 50% compared with the state-of-the-art Spiral.

This article introduces an innovative design of a low-pass (LP) negative group delay (NGD) integrated circuit (IC) in the 180-nm CMOS technology. The LP-NGD circuit is an inductorless topology constituted by RC-network with CMOS metal-insulator-metal (MIM) capacitor and polygate resistor. The design methodology is illustrated by considering the chip layout process. Then, the first run simulation is performed with the design rule check (DRC) and 2.5 mm${\times }$2.2 mm layout versus schematic (LVS) approaches. The feasibility of the CMOS LP-NGD IC circuit implementation is validated with chip-onboard (CoB). The proof of concept (PoC) of the LP-NGD miniaturized circuit was tested in both S-parameter and time domain (TD). As expected, the calculated, simulated, and experimented results of CoB showing NGD of about −10 ns over 12 MHz and −10 dB attenuation are confirmed. The active CMOS LP-NGD technology compensates the insertion loss to 2.4 dB, the GD reaches −11 ns, and the reflection loss reaches −20 dB. Moreover, TD investigations were also performed to show the feasibility of generating pulse and arbitrary waveform signal time advance through the designed and fabricated LP-NGD CoB prototypes.

The scattering fields of 2D sea fractal surface with finite conductivity illuminated by ellipse polarization wave in Cartesian coordinate system have been evaluated in part one. We derive here the relation expression between scattering fields and d illumination fields with 3/spl times/3 matrix in local coordinate system. The radar cross section (RCS) on different polarization is obtained and numerically simulated. It shows that the results of our scattering model are in agreement with those of other literatures for some special case. We get some conclusions: (1) valued of radar cross sections of cross polarization (VH and HV) are less than those of co-polarization (VV and HH) but cannot be neglected; (2) when the incidence angle /spl theta//sub 1/, and the scattering angle /spl theta//sub 2/ are determined, the angle of the scattering plane out of the illuminating plane /spl theta//sub 3/ varies from 0/spl deg/ to 180/spl deg/, different relations among /spl theta//sub 1/, /spl theta//sub 2/ and /spl theta//sub 3/ in different relationships between /spl sigma//sub vs,vt//sup 0/, /spl sigma//sub h/spl delta//,h/sub i//sup 0/ and /spl sigma//sub v/spl delta//,h/sub i//sup 0/, /spl sigma//sub h/spl delta//,v/sub i//sup 0/ are derived, we can use these inequalities to predict the critical angle /spl theta//sub 3/ where the relation between RCS of VV and HH,VH and HV polarization will exchange, respectively; (3) the effects of depolarization can be neglected though we derived the expressions for them.

Recently, many analytical expressions of scattering fields of sea fractal surface with infinite conductivity were derived. In order to simulate multi-polarization SAR imaging of sea surface and consider the effects of polarization on remote sensing of sea surface, we derive the scattering fields from 2D sea fractal surface with finite conductivity illuminated by ellipse polarization wave at Kirchhoff approximation. Then we present the scattering matrix of this model and numerically simulate the bistatic radar cross section (RCS) of 2D sea fractal surface. It shows that the result of applying our model coincides with that of relevant literatures. Our work is divided into two parts. In the first part, we derive the scattering fields in Cartesian coordinates. And in the second part, we evaluate the scattering matrix of this model and then give the numerical results and discuss them.