B+-tree Index Optimization by Exploiting Internal Parallelism of Flash-based Solid State Drives

Previous research addressed the potential problems of the hard-disk oriented design of DBMSs of flashSSDs. In this paper, we focus on exploiting potential benefits of flashSSDs. First, we examine the internal parallelism issues of flashSSDs by conducting benchmarks to various flashSSDs. Then, we suggest algorithm-design principles in order to best benefit from the internal parallelism. We present a new I/O request concept, called psync I/O that can exploit the internal parallelism of flashSSDs in a single process. Based on these ideas, we introduce B+-tree optimization methods in order to utilize internal parallelism. By integrating the results of these methods, we present a B+-tree variant, PIO B-tree. We confirmed that each optimization method substantially enhances the index performance. Consequently, PIO B-tree enhanced B+-tree's insert performance by a factor of up to 16.3, while improving point-search performance by a factor of 1.2. The range search of PIO B-tree was up to 5 times faster than that of the B+-tree. Moreover, PIO B-tree outperformed other flash-aware indexes in various synthetic workloads. We also confirmed that PIO B-tree outperforms B+-tree in index traces collected inside the Postgresql DBMS with TPC-C benchmark.Comment: VLDB201

On the use of asymmetric PSF on NIR images of crowded stellar fields

We present data collected using the camera PISCES coupled with the Firt Light Adaptive Optics (FLAO) mounted at the Large Binocular Telescope (LBT). The images were collected using two natural guide stars with an apparent magnitude of R<13 mag. During these observations the seeing was on average ~0.9". The AO performed very well: the images display a mean FWHM of 0.05 arcsec and of 0.06 arcsec in the J- and in the Ks-band, respectively. The Strehl ratio on the quoted images reaches 13-30% (J) and 50-65% (Ks), in the off and in the central pointings respectively. On the basis of this sample we have reached a J-band limiting magnitude of ~22.5 mag and the deepest Ks-band limiting magnitude ever obtained in a crowded stellar field: Ks~23 mag. J-band images display a complex change in the shape of the PSF when moving at larger radial distances from the natural guide star. In particular, the stellar images become more elongated in approaching the corners of the J-band images whereas the Ks-band images are more uniform. We discuss in detail the strategy used to perform accurate and deep photometry in these very challenging images. In particular we will focus our attention on the use of an updated version of ROMAFOT based on asymmetric and analytical Point Spread Functions. The quality of the photometry allowed us to properly identify a feature that clearly shows up in NIR bands: the main sequence knee (MSK). The MSK is independent of the evolutionary age, therefore the difference in magnitude with the canonical clock to constrain the cluster age, the main sequence turn off (MSTO), provides an estimate of the absolute age of the cluster. The key advantage of this new approach is that the error decreases by a factor of two when compared with the classical one. Combining ground-based Ks with space F606W photometry, we estimate the absolute age of M15 to be 13.70+-0.80 Gyr.Comment: 15 pages, 7 figures, presented at the SPIE conference 201

A Meaningful MD5 Hash Collision Attack

It is now proved by Wang et al., that MD5 hash is no more secure, after they proposed an attack that would generate two different messages that gives the same MD5 sum. Many conditions need to be satisfied to attain this collision. Vlastimil Klima then proposed a more efficient and faster technique to implement this attack. We use these techniques to first create a collision attack and then use these collisions to implement meaningful collisions by creating two different packages that give identical MD5 hash, but when extracted, each gives out different files with contents specified by the atacker

How private is private information?:The ability to spot deception in an economic game

We provide experimental evidence on the ability to detect deceit in a buyer-seller game with asymmetric information. Sellers have private information about the buyer's valuation of a good and sometimes have incentives to mislead buyers. We examine if buyers can spot deception in face-to-face encounters. We vary (1) whether or not the buyer can interrogate the seller, and (2) the contextual richness of the situation. We find that the buyers' prediction accuracy is above chance levels, and that interrogation and contextual richness are important factors determining the accuracy. These results show that there are circumstances in which part of the information asymmetry is eliminated by people's ability to spot deception

The asymmetric simple exclusion process: an integrable model for non-equilibrium statistical mechanics

The asymmetric simple exclusion process (ASEP) plays the role of a paradigm in non-equilibrium statistical mechanics. We review exact results for the ASEP obtained by Bethe ansatz and put emphasis on the algebraic properties of this model. The Bethe equations for the eigenvalues of the Markov matrix of the ASEP are derived from the algebraic Bethe ansatz. Using these equations we explain how to calculate the spectral gap of the model and how global spectral properties such as the existence of multiplets can be predicted. An extension of the Bethe ansatz leads to an analytic expression for the large deviation function of the current in the ASEP that satisfies the Gallavotti-Cohen relation. Finally, we describe some variants of the ASEP that are also solvable by Bethe ansatz. Keywords: ASEP, integrable models, Bethe ansatz, large deviations.Comment: 24 pages, 5 figures, published in the "special issue on recent advances in low-dimensional quantum field theories", P. Dorey, G. Dunne and J. Feinberg editor

Collective identities, European solidarity : identification patterns and preferences for European social Insurance

A degree of collective identity is often perceived to be a requirement for integration of core state powers, and even more so when redistributive measures are at stake. Existing research has shown that European identity is an important correlate of support for European social policy in general. This article explores the ways in which collective identities relate to the multidimensional nature of social policy at the European level. We explore in particular the features of European social policy that receive the most support from European publics, and how local, national and European identity moderates these preferences. We expect that people who have primarily sub-national or national attachments are less supportive of generous schemes and schemes that involve greater cross-country redistribution, and are more in favour of decentralized schemes administered by the member states than those with stronger European identities. We find support for these expectations in a conjoint survey experiment fielded in autumn 2018 in 13 EU member states

Recent developments of MCViNE and its applications at SNS

MCViNE is an open source, object-oriented Monte Carlo neutron ray-tracing simulation software package. Its design allows for flexible, hierarchical representations of sophisticated instrument components such as detector systems, and samples with a variety of shapes and scattering kernels. Recently this flexible design has enabled several applications of MCViNE simulations at the Spallation Neutron Source (SNS) at Oak Ridge National Lab, including assisting design of neutron instruments at the second target station and design of novel sample environments, as well as studying effects of instrument resolution and multiple scattering. Here we provide an overview of the recent developments and new features of MCViNE since its initial introduction (Jiao et al 2016 Nucl. Instrum. Methods Phys. Res., Sect. A 810, 86–99), and some example applications