Ground-state configurations in ferromagnetic nanotori

Magnetization ground states are studied in toroidal nanomagnets. The energetics associated to the ferromagnetic, vortex and onion-like configurations are explicitly computed. The analysis reveals that the vortex appears to be the most prominent of such states, minimizing total energy in every torus with internal radius $r\gtrsim10\,{\rm nm}$ (for Permalloy). For $r\lesssim10\,{\rm nm}$ the vortex remains the most favorable pattern whenever $R/\ell_{ex}\gtrsim1.5$ ($R$ is the torus external radius and $\ell_{ex}$ is the exchange length), being substituted by the ferromagnetic state whenever $R/\ell_{ex}\lesssim1.5$.Comment: 16 pages, 9 figures, 3 apendices, Revtex forma

A new design principle of robust onion-like networks self-organized in growth

Today's economy, production activity, and our life are sustained by social and technological network infrastructures, while new threats of network attacks by destructing loops have been found recently in network science. We inversely take into account the weakness, and propose a new design principle for incrementally growing robust networks. The networks are self-organized by enhancing interwoven long loops. In particular, we consider the range-limited approximation of linking by intermediations in a few hops, and show the strong robustness in the growth without degrading efficiency of paths. Moreover, we demonstrate that the tolerance of connectivity is reformable even from extremely vulnerable real networks according to our proposed growing process with some investment. These results may indicate a prospective direction to the future growth of our network infrastructures.Comment: 21 pages, 10 figures, 1 tabl

HORNET: High-speed Onion Routing at the Network Layer

We present HORNET, a system that enables high-speed end-to-end anonymous channels by leveraging next generation network architectures. HORNET is designed as a low-latency onion routing system that operates at the network layer thus enabling a wide range of applications. Our system uses only symmetric cryptography for data forwarding yet requires no per-flow state on intermediate nodes. This design enables HORNET nodes to process anonymous traffic at over 93 Gb/s. HORNET can also scale as required, adding minimal processing overhead per additional anonymous channel. We discuss design and implementation details, as well as a performance and security evaluation.Comment: 14 pages, 5 figure

Growth and competition model for organic weed control

There is a more detailed Executive Summary at the top of the attached document, which is the final report for Defra Project OF0177. The project aimed to examine the organic extension of a simple mechanistically-based growth and competition model, calibrated to data originally gained from conventional vegetable production. Essentially the model simulation follows the growth of each crop and weed plant as they compete for space and light during and after canopy closure. The growth and competition model has been modified to simulate crop and weed growth of multiple cohorts so that the onset of crop weed competition can be predicted. This onset of competition marks the point when it is essential to remove weeds (i.e. critical weeding time); otherwise, there will be a penalty to crop yield. The model can be applied to determine the onset of competition between competing species (i.e. crop and weed). In organic crops this would be the time when physical removal of the weeds (either by means of mechanical or hand weeding methods) was essential to prevent yield loss. To test the ability of the model to identify critical weeding times, model predictions were compared with historical experimental data. The inputs to the model are starting plant weights and the numbers of individuals per unit area of the crop and weed species for each cohort at each day of the simulation. Solar radiation was used to drive the model. All the growth parameters were species specific and where a number of weed species are competing with the crop in a mixed population, then a general set of parameters representing the mean of a range of parameterised weed species were used. Repeatedly running the simulation with different starting inputs from a range of historical data sets indicated that the observed critical weeding time was described well by the model. To examine the applicability of the principle of the growth model to an organic cropping situation, the predicted optimum timing of weed removal simulated by the model was incorporated as a treatment into an existing organic carrot trial. The aim was to see whether the weeding time simulated by the model achieved comparable or better results than the weeding by the unaided judgement of the grower.The results demonstrated that there was certainly no disadvantage to using the model in that year to aid in the decision making process. A small-scale trial was made in year 3, incluing cabbage plus three previously unparameterised crops; broccoli, cauliflower and leeks. The crop parameters for cabbage were used to drive the cauliflower and broccoli simulations and onion parameters for leeks. Three treatments were; weeding once as recommended by advisors at HDRA, weeding once as predicted by the model and left weedy throughout to test the competitive level of the weed flora. Inputs into the model were solar radiation, crop transplant weights and numbers, and weed weights and numbers during the early weeks of crop growth. Adjustment of the model using the final crop weights was related to the different relative growth rates of the crops in organic soils, compared with the higher N levels in conventional soils from where the parameters had been originally derived. After recalibration, the model re-confirmed the mid-August onset of competition, but tended to over predict the degree of weed competition. The notable exception was the leek crop which was more sensitive to competition than its brassica counterparts and gave a good illustration of the potential power of the model. As part of the project several presentations have been made to growers during the final year, which have allowed a dialogue and awareness to develop highlighting the practical and scientific implications of the model

How Unique is Your .onion? An Analysis of the Fingerprintability of Tor Onion Services

Recent studies have shown that Tor onion (hidden) service websites are particularly vulnerable to website fingerprinting attacks due to their limited number and sensitive nature. In this work we present a multi-level feature analysis of onion site fingerprintability, considering three state-of-the-art website fingerprinting methods and 482 Tor onion services, making this the largest analysis of this kind completed on onion services to date. Prior studies typically report average performance results for a given website fingerprinting method or countermeasure. We investigate which sites are more or less vulnerable to fingerprinting and which features make them so. We find that there is a high variability in the rate at which sites are classified (and misclassified) by these attacks, implying that average performance figures may not be informative of the risks that website fingerprinting attacks pose to particular sites. We analyze the features exploited by the different website fingerprinting methods and discuss what makes onion service sites more or less easily identifiable, both in terms of their traffic traces as well as their webpage design. We study misclassifications to understand how onion service sites can be redesigned to be less vulnerable to website fingerprinting attacks. Our results also inform the design of website fingerprinting countermeasures and their evaluation considering disparate impact across sites.Comment: Accepted by ACM CCS 201