Discrete Gaussian Measures and New Bounds of the Smoothing Parameter for Lattices

In this paper, we start with a discussion of discrete Gaussian measures on lattices. Several results of Banaszczyk are analyzed, different approaches are suggested. In the second part of the paper we prove two new bounds for the smoothing parameter of lattices. Under the natural assumption that $\varepsilon$ is suitably small, we obtain two estimations of the smoothing parameter: 1. $$\eta_{\varepsilon}(\mathbb{Z}) \le \sqrt{\frac{\ln \big(\frac{\varepsilon}{44}+\frac{2}{\varepsilon}\big)}{\pi}}.$$ 2. For a lattice ${\cal L}\subset \mathbb{R}^n$ of dimension $n$, \[ \eta_{\varepsilon}({\cal L}) \le \sqrt{\frac{\ln \big(n-1+\frac{2n}{\varepsilon}\big)}{\pi}}\tilde{bl}({\cal L}). \

The Lifecycle of Semidiurnal Internal Tides over the Northern Mid-Atlantic Ridge

The lifecycle of semidiurnal internal tides over the Mid-Atlantic Ridge (MAR) sector south of the Azores is investigated using in situ, a high-resolution mooring and microstructure profiler, and satellite data, in combination with a theoretical model of barotropic-to-baroclinic tidal energy conversion. The mooring analysis reveals that the internal-tide horizontal energy flux is dominated by mode 1, and that energy density is more distributed among modes 1-10. Most modes are compatible with an interpretation in terms of standing internal tides, suggesting that they result from interactions between waves generated over the MAR. Internal tide energy is thus concentrated above the ridge and is eventually available for local diapycnal mixing, as endorsed by the elevated rates of turbulent energy dissipation, ε, estimated from microstructure measurements. A spring-neap modulation of energy density on the MAR is found to originate from the remote generation and radiation of strong mode-1 internal tides from the Atlantis Meteor Seamount Complex. Similar fortnightly variability of a factor of 2 is observed in ε, but this signal’s origin cannot be determined unambiguously. A regional tidal energy budget highlights the significance of high-mode generation, with 81% of the energy lost by the barotropic tide being converted into modes > 1, and only 9% into mode 1. This has important implications for the fraction of local dissipation to the total energy conversion, q, which is regionally estimated to be ~0.5. This result is in stark contrast with the Hawaiian Ridge system, where the radiation of mode-1 internal tides accounts for 30% of the regional energy conversion, and q < 0.25

Distinguishing LWE Instances Using Fourier Transform: A Refined Framework and its Applications

As a fundamental tool in lattice-based cryptosystems, discrete Gaussian samplers play important roles in both efficiency and security of lattice-based schemes. Approximate discrete rounded Gaussian sampler, central binomial sampler and bounded uniform sampler are three types of error samplers that are commonly used in the designs of various schemes. However, known cryptanalytics about error samplers concentrate on their standard deviations and no analysis about distinct structures of distributions have been proposed. In this paper, we address this problem by considering the dual attack for LWE instances and investigating Fourier transforms of these distributions. We introduce the concept of local width which enables us to get a more detailed look of these distributions and the distinguish advantages. We make an analysis of dual attack for different distributions and provide a novel measure model to describe the differences. Within this refined framework, we also propose a novel type of error sampler which can achieve high efficiency, security as well as flexibility

A Key Backup Scheme Based on Bitcoin

Since first introduced by Satoshi Nakamoto in 2008, Bitcoin has become the biggest and most well-known decentralized digital currency. Its anonymity allows users all over the world to make transactions with each other and keep their identities hidden. However, protecting private key becomes a very important issue because it is the only access to a unique account and can hardly be recovered if missing. Storing an encrypted backup of private key and its corresponding advanced key is a traditional but effective way, and many other techniques help to make the backup harder to obtain by attackers. While in this paper, we introduce a new backup scheme that can provide protection when an attacker manages to obtain the backup. It is based on Bitcoin system and ECDSA signature scheme. The biggest difference is the generation and recovery of the backup processes are both related with some specific transactions on blockchain, thus it creates a gap for legal users and attackers who manages to obtain backup to recover key. The gap is decided by the number of accounts and transactions on the blockchain which increases rapidly with the growth of Bitcoin\u27s popularity and therefore strengthens the security of our scheme at the same time. What\u27s more, our technique can also be combined with former ones to achieve better security

Sealing of oil-gas reservoir caprock: Destruction of shale caprock by micro-fractures

The sealing ability of caprock is affected by many factors, such as cap thickness, displacement pressure, fracture development, and lithology of caprock. Shale is one of the ideal materials for oil and gas sealing cap formation due to its low porosity and permeability. Microfractures can destroy the sealing property of shale caprock. When buried deep enough, shale will change from toughness to brittleness. In general, the greater the brittleness of shale, the more developed the fractures will be. In areas with high tectonic stress, such as the anticline axis, syncline axis and stratum dip end, the strata stress is high and concentrated, and it is easier to generate fractures. When the stress state of the caprock changes, new micro-cracks are formed or previously closed cracks are re-opened, reducing the displacement pressure of the caprock. These micro-fractures are interconnected to form microleakage spaces, which reduces the sealing capacity of the caprock

Continental interior and edge breakup at convergent margins induced by subduction direction reversal: a numerical modeling study applied to the South China Sea margin

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Tectonics 39(11), (2020): e2020TC006409, doi:10.1029/2020TC006409.The dynamics of continental breakup at convergent margins has been described as the results of backarc opening caused by slab rollback or drag force induced by subduction direction reversal. Although the rollback hypothesis has been intensively studied, our understanding of the consequence of subduction direction reversal remains limited. Using thermo‐mechanical modeling based on constraints from the South China Sea (SCS) region, we investigate how subduction direction reversal controls the breakup of convergent margins. The numerical results show that two distinct breakup modes, namely, continental interior and edge breakup (“edge” refers to continent above the plate boundary interface), may develop depending on the “maturity” of the convergent margin and the age of the oceanic lithosphere. For a slab age of ~15 to ~45 Ma, increasing the duration of subduction promotes the continental interior breakup mode, where a large block of the continental material is separated from the overriding plate. In contrast, the continental edge breakup mode develops when the subduction is a short‐duration event, and in this mode, a wide zone of less continuous continental fragments and tearing of the subducted slab occur. These two modes are consistent with the interior (relic late Mesozoic arc) and edge (relic forearc) rifting characteristics in the western and eastern SCS margin, suggesting that variation in the northwest‐directed subduction duration of the Proto‐SCS might be a reason for the differential breakup locus along the strike of the SCS margin. Besides, a two‐segment trench associated with the northwest‐directed subduction is implied in the present‐day SCS region.This research was supported by the Guangdong NSF research team project (2017A030312002), the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0205), the K. C. Wong Education Foundation (GJTD‐2018‐13), the Strategic Priority Research Program of the Chinese Academy of Science (XDA13010303), the Chinese Academy of Sciences (Y4SL021001, QYZDY‐SSWDQC005, 133244KYSB20180029, and ISEE2019ZR01), the NSFC project (41606073, 41890813, and 41576070), the IODP‐China Foundation, the OMG Visiting Fellowship (OMG18‐15), and the Hong Kong Research Grant Council Grants (Nos. 14313816 and 14304820).2021-04-0

A Secure Hybrid Duplex Relay System with Joint Optimization of Finite Blocklength and Power

As mission-critical Internet of Things (MC-IoT) is expected to carry important and private information, its high quality of service (QoS) and high physical layer (PHY) security are indispensable. Nevertheless, most existing PHY security related work is built on the assumption of infinite blocklength, which is not applicable to finite blocklength (FBL) transmission, a typical scenario in MC-IoT such as factory automation. In this paper, we address the PHY security issue of a hybrid duplex relay aided MC-IoT system with FBL. Closed-form expressions for statistical secrecy throughput of full-duplex (FD) and half-duplex (HD) relay systems are derived, respectively, which are verified by numerical results. Based on the closed-form secrecy throughput, joint optimization of blocklength and transmission powers at source and relay is conducted for FD and HD relay systems, respectively. A hybrid duplex relaying scheme is also proposed by selecting the duplex mode with a higher achievable secrecy throughput. Numerical results show that, together with the hybrid relaying scheme, the proposed relay system with joint power allocation and blocklength adaptation, relay mode selection achieves much higher secrecy throughput over the conventional sole FD or HD mode relaying systems. Also, it is revealed that increasing blocklength or transmitting power may not always lead to a higher secrecy throughput and energy efficiency (EE)