Soil microbiology

RESP-385

Skeleton Cave, Leigh Woods, Bristol

An account is given of the discovery and excavation of this small cave in the 1960s. It is recorded that archaeological finds were made, but of these, only a single human mandible can now be traced. Radiocarbon dating shows the specimen to be early Neolithic in age; a metrical analysis was less conclusive.http://www.ubss.org.uk/resources/proceedings/vol27/UBSS_Proc_27_2_197-209.pd

Aggregatable Distributed Key Generation

In this paper, we introduce a distributed key generation (DKG) protocol with aggregatable and publicly-verifiable transcripts. Compared with prior publicly-verifiable approaches, our DKG reduces the size of the final transcript and the time to verify it from O(n2) to O(nlogn) , where n denotes the number of parties. As compared with prior non-publicly-verifiable approaches, our DKG leverages gossip rather than all-to-all communication to reduce verification and communication complexity. We also revisit existing DKG security definitions, which are quite strong, and propose new and natural relaxations. As a result, we can prove the security of our aggregatable DKG as well as that of several existing DKGs, including the popular Pedersen variant. We show that, under these new definitions, these existing DKGs can be used to yield secure threshold variants of popular cryptosystems such as El-Gamal encryption and BLS signatures. We also prove that our DKG can be securely combined with a new efficient verifiable unpredictable function (VUF), whose security we prove in the random oracle model. Finally, we experimentally evaluate our DKG and show that the per-party overheads scale linearly and are practical. For 64 parties, it takes 71 ms to share and 359 ms to verify the overall transcript, while for 8192 parties, it takes 8 s and 42.2 s respectively

A Fistful of Bitcoins: Characterizing Payments among Men with No Names

Bitcoin is a purely online virtual currency, unbacked by either physical commodities or sovereign obligation; instead, it relies on a combination of cryptographic protection and a peer-to-peer protocol for witnessing settlements. Consequently, Bitcoin has the unintuitive property that while the ownership of money is implicitly anonymous, its flow is globally visible. In this paper we explore this unique characteristic further, using heuristic clustering to group Bitcoin wallets based on evidence of shared authority, and then using re-identification attacks (i.e., empirical purchasing of goods and services) to classify the operators of those clusters. From this analysis, we consider the challenges for those seeking to use Bitcoin for criminal or fraudulent purposes at scale

SoK: Consensus in the Age of Blockchains

The core technical component of blockchains is consensus: how to reach agreement among a distributed network of nodes. A plethora of blockchain consensus protocols have been proposed---ranging from new designs, to novel modifications and extensions of consensus protocols from the classical distributed systems literature. The inherent complexity of consensus protocols and their rapid and dramatic evolution makes it hard to contextualize the design landscape. We address this challenge by conducting a systematization of knowledge of blockchain consensus protocols. After first discussing key themes in classical consensus protocols, we describe: (i) protocols based on proof-of-work; (ii) proof-of-X protocols that replace proof-of-work with more energy-efficient alternatives; and (iii) hybrid protocols that are compositions or variations of classical consensus protocols. This survey is guided by a systematization framework we develop, to highlight the various building blocks of blockchain consensus design, along with a discussion on their security and performance properties. We identify research gaps and insights for the community to consider in future research endeavours

Metastable Random Field Ising model with exchange enhancement: a simple model for Exchange Bias

We present a simple model that allows hysteresis loops with exchange bias to be reproduced. The model is a modification of the T=0 random field Ising model driven by an external field and with synchronous local relaxation dynamics. The main novelty of the model is that a certain fraction f of the exchange constants between neighbouring spins is enhanced to a very large value J_E. The model allows the dependence of the exchange bias and other properties of the hysteresis loops to be analyzed as a function of the parameters of the model: the fraction f of enhanced bonds, the amount of the enhancement J_E and the amount of disorder which is controlled by the width sigma of the Gaussian distribution of the random fields.Comment: 8 pages, 11 figure

Quisquis: A new design for anonymous cryptocurrencies

Despite their usage of pseudonyms rather than persistent identifiers, most existing cryptocurrencies do not provide users with any meaningful levels of privacy. This has prompted the creation of privacy-enhanced cryptocurrencies such as Monero and Zcash, which are specifically designed to counteract the tracking analysis possible in currencies like Bitcoin. These cryptocurrencies, however, also suffer from some drawbacks: in both Monero and Zcash, the set of potential unspent coins is always growing, which means users cannot store a concise representation of the blockchain. Additionally, Zcash requires a common reference string and the fact that addresses are reused multiple times in Monero has led to attacks to its anonymity. In this paper we propose a new design for anonymous cryptocurrencies, Quisquis, that achieves provably secure notions of anonymity. Quisquis stores a relatively small amount of data, does not require trusted setup, and in Quisquis each address appears on the blockchain at most twice: once when it is generated as output of a transaction, and once when it is spent as input to a transaction. Our result is achieved by combining a DDH-based tool (that we call updatable keys) with efficient zero-knowledge arguments

Ferromagnetic Domain Distribution in Thin Films During Magnetization Reversal

We have shown that polarized neutron reflectometry can determine in a model-free way not only the mean magnetization of a ferromagnetic thin film at any point of a hysteresis cycle, but also the mean square dispersion of the magnetization vectors of its lateral domains. This technique is applied to elucidate the mechanism of the magnetization reversal of an exchange-biased Co/CoO bilayer. The reversal process above the blocking temperature is governed by uniaxial domain switching, while below the blocking temperature the reversal of magnetization for the trained sample takes place with substantial domain rotation

The Effect of Age and Occupation on the Seroprevalence of Helicobacter pylori

Serological studies in developed and developing countries using enzyme-linked immunosorbent assays have validated this technique as a rapid, noninvasive method for the diagnosis of Helicobacter pylori infections. The prevalence of serum antibodies to H pylori was studied in 473 Canadian blood donors from Manitoba, 212 healthy Japanese. and 226 healthy Americans. As expected, the seroprevalence rose progressively with age in the three populations and reached its peak (greater than 55%) in subjects 60 years of age and older. The seroprevalence did not decrease in elderly persons (60 to 99 years), indicating a persistent immune response. More detailed analysis was perfom1ed on the Canadian population. Age-adjusted prevalence rates in men and women were similar. Among young adults (15 to 29 years). farmers had a significantly higher seroprevalence rate than white-collar or blue-collar workers. but in older persons occupational rates were similar. A multiple linear regression analysis of the data confirmed that age and occupation in young adults were both significantly associated with seroprevalence of H pylori infections