Efficient algorithms for pairing-based cryptosystems

We describe fast new algorithms to implement recent cryptosystems based on the Tate pairing. In particular, our techniques improve pairing evaluation speed by a factor of about 55 compared to previously known methods in characteristic 3, and attain performance comparable to that of RSA in larger characteristics.We also propose faster algorithms for scalar multiplication in characteristic 3 and square root extraction over Fpm, the latter technique being also useful in contexts other than that of pairing-based cryptography

An assessment of pile driveability analyses for monopile foundations

Several methodologies to predict the static soil resistance to driving (SRD) available in the literature have found wide use in the offshore industry over the last decades. These range from simple methods that require few soil strength parameters to more advanced semi-empirical methods that correlate the driving resistance to cone penetration test measurements. These methods were primarily developed based on driving records for piles less than 2.5m in diameter i.e. much smaller than the monopiles currently used in the offshore wind industry today. The aim of this study is to evaluate the accuracy of some of the most widely used SRD prediction methods when employed for driveability analysis of large diameter monopile foundations, by comparing the predicted SRD profiles with the driving records of 6.5m diameter monopiles installed in the Danish region of the North Sea

An Economic Study of the Effect of Android Platform Fragmentation on Security Updates

Vendors in the Android ecosystem typically customize their devices by modifying Android Open Source Project (AOSP) code, adding in-house developed proprietary software, and pre-installing third-party applications. However, research has documented how various security problems are associated with this customization process. We develop a model of the Android ecosystem utilizing the concepts of game theory and product differentiation to capture the competition involving two vendors customizing the AOSP platform. We show how the vendors are incentivized to differentiate their products from AOSP and from each other, and how prices are shaped through this differentiation process. We also consider two types of consumers: security-conscious consumers who understand and care about security, and na\"ive consumers who lack the ability to correctly evaluate security properties of vendor-supplied Android products or simply ignore security. It is evident that vendors shirk on security investments in the latter case. Regulators such as the U.S. Federal Trade Commission have sanctioned Android vendors for underinvestment in security, but the exact effects of these sanctions are difficult to disentangle with empirical data. Here, we model the impact of a regulator-imposed fine that incentivizes vendors to match a minimum security standard. Interestingly, we show how product prices will decrease for the same cost of customization in the presence of a fine, or a higher level of regulator-imposed minimum security.Comment: 22nd International Conference on Financial Cryptography and Data Security (FC 2018

On the morphological deviation in additive manufacturing of porous Ti6Al4V scaffold: a design consideration

Additively manufactured Ti scaffolds have been used for bone replacement and orthopaedic applications. In these applications, both morphological and mechanical properties are important for their in vivo performance. Additively manufactured Ti6Al4V triply periodic minimal surface (TPMS) scaffolds with diamond and gyroid structures are known to have high stiffness and high osseointegration properties, respectively. However, morphological deviations between the as-designed and as-built types of these scaffolds have not been studied before. In this study, the morphological and mechanical properties of diamond and gyroid scaffolds at macro and microscales were examined. The results demonstrated that the mean printed strut thickness was greater than the designed target value. For diamond scaffolds, the deviation increased from 7.5 μm (2.5% excess) for vertical struts to 105.4 μm (35.1% excess) for horizontal struts. For the gyroid design, the corresponding deviations were larger, ranging from 12.6 μm (4.2% excess) to 198.6 μm (66.2% excess). The mean printed pore size was less than the designed target value. For diamonds, the deviation of the mean pore size from the designed value increased from 33.1 μm (-3.0% excess) for vertical struts to 92.8 μm (-8.4% excess) for horizontal struts. The corresponding deviation for gyroids was larger, ranging from 23.8 μm (-3.0% excess) to 168.7 μm (-21.1% excess). Compressive Young's modulus of the bulk sample, gyroid and diamond scaffolds was calculated to be 35.8 GPa, 6.81 GPa and 7.59 GPa, respectively, via the global compression method. The corresponding yield strength of the samples was measured to be 1012, 108 and 134 MPa. Average microhardness and Young's modulus from α and β phases of Ti6Al4V from scaffold struts were calculated to be 4.1 GPa and 131 GPa, respectively. The extracted morphology and mechanical properties in this study could help understand the deviation between the as-design and as-built matrices, which could help develop a design compensation strategy before the fabrication of the scaffolds

Population Genetic Structure of Aldabra Giant Tortoises

Evolution of population structure on islands is the result of physical processes linked to volcanism, orogenic events, changes in sea level, as well as habitat variation. We assessed patterns of genetic structure in the giant tortoise of the Aldabra atoll, where previous ecological studies suggested population subdivisions as a result of landscape discontinuity due to unsuitable habitat and island separation. Analysis of mitochondrial DNA (mtDNA) control region sequences and allelic variation at 8 microsatellite loci were conducted on tortoises sampled in 3 locations on the 2 major islands of Aldabra. We found no variation in mtDNA sequences. This pattern corroborated earlier work supporting the occurrence of a founding event during the last interglacial period and a further reduction in genetic variability during historical time. On the other hand, significant population structure recorded at nuclear loci suggested allopatric divergence possibly due to geographical barriers among islands and ecological partitions hindering tortoise movements within islands. This is the first attempt to study the population genetics of Aldabra tortoises, which are now at carrying capacity in an isolated terrestrial ecosystem where ecological factors appear to have a strong influence on population dynamic

Reaction physics and mission capabilities of the magnetically insulated inertial confinement fusion reactor

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76048/1/AIAA-25451-882.pd

A new stall-onset criterion for low speed dynamic-stall

The Beddoes/Leishman dynamic-stall model has become one of the most popular for the provision of unsteady aerofoil data embedded in much larger codes. The underlying modeling philosophy was that it should be based on the best understanding, or description, of the associated physical phenomena. Even though the model was guided by the flow physics, it requires significant empirical inputs in the form of measured coefficients and constants. Beddoes provided these for a Mach number range of 0.3–0.8. This paper considers one such input for a Mach number of 0.12, where, from the Glasgow data, it is shown that the current stall-onset criterion, and subsequent adjustments, yield problematic results. A new stall criterion is proposed and developed in the best traditions of the model. It is shown to be very capable of reconstructing the Glasgow's data for stall onset both the ramp-up and oscillatory tests

Beam position monitor offset determination at LEP

For the performance of an electron positron storage ring it is important that the beam orbit passes well centred through the quadrupole magnets. Beam position monitors (BPM) aligned relative to the magnets can still have a residual mechanical or electronical offset with respect to the magnetic axis. A beam-based method is used at LEP to measure these offsets. During the machine operation for physics the gradient of selected quadrupoles is modulated with low frequencies (few Hz) and very small amplitudes (of the order of 10-4). The effect on the beam is observed with a high sensitivity pick-up. The observed effect passes through a minimum when the beam is centred in the quadrupole. Offsets for about 70 different BPM's were determined. Systematically different offsets were found for different type of BPM electronics and different types of quadrupoles. Simulations based on the past results show that the level of spin polarisation can be increased by further offset measurements

Visualizing MCNP Tally Segment Geometry and Coupling Results with ABAQUS

The Advanced Graphite Creep test, AGC-1, is planned for irradiation in the Advanced Test Reactor (ATR) in support of the Next Generation Nuclear Plant program. The experiment requires very detailed neutronics and thermal hydraulics analyses to show compliance with programmatic and ATR safety requirements. The MCNP model used for the neutronics analysis required hundreds of tally regions to provide the desired detail. A method for visualizing the hundreds of tally region geometries and the tally region results in 3 dimensions has been created to support the AGC-1 irradiation. Additionally, a method was created which would allow ABAQUS to access the results directly for the thermal analysis of the AGC-1 experiment

Statistics for Fission-Track Thermochronology

This chapter introduces statistical tools to extract geologically meaningful information from fission-track (FT) data using both the external detector and LA-ICP-MS methods. The spontaneous fission of 238U is a Poisson process resulting in large single-grain age uncertainties. To overcome this imprecision, it is nearly always necessary to analyse multiple grains per sample. The degree to which the analytical uncertainties can explain the observed scatter of the single-grain data can be visually assessed on a radial plot and objectively quantified by a chi-square test. For sufficiently low values of the chi-square statistic (or sufficiently high p values), the pooled age of all the grains gives a suitable description of the underlying ‘true’ age population. Samples may fail the chi-square test for several reasons. A first possibility is that the true age population does not consist of a single discrete age component, but is characterised by a continuous range of ages. In this case, a ‘random effects’ model can constrain the true age distribution using two parameters: the ‘central age’ and the ‘(over)dispersion’. A second reason why FT data sets might fail the chi-square test is if they are underlain by multimodal age distributions. Such distributions may consist of discrete age components, continuous age distributions, or a combination of the two. Formalised statistical tests such as chi-square can be useful in preventing overfitting of relatively small data sets. However, they should be used with caution when applied to large data sets (including length measurements) which generate sufficient statistical ‘power’ to reject any simple yet geologically plausible hypothesis