Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

Highly-parallelized simulation of a pixelated LArTPC on a GPU

The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype

Comparative evaluation of semi-fragile JPEG watermarking methods

Одним из способов защиты изображений от подделки является встраивание в них цифровых водяных знаков (ЦВЗ) – добавочной информации, разрушающейся при внесении несанкционированных изменений. Отдельной сложностью при проектировании алгоритмов встраивания подобных ЦВЗ является обеспечение их стойкости к допустимым преобразованиям, наиболее характерным примером которых является сжатие с потерями. Такие ЦВЗ называются полухрупкими. Настоящая работа посвящена исследованию различных алгоритмов встраивания ЦВЗ, проявляющих себя как полухрупкие по отношению к JPEG-сжатию. Интерес представляет исследование влияния объёма встраиваемой информации, местоположения отбираемых для встраивания спектральных коэффициентов, а также конкретных методов их модификации на качество результирующего (защищённого) изображения, а также на точность решения искомой задачи аутентификации. Данное исследование проведено с целью выработки рекомендаций по выбору сочетаний этих параметров в зависимости от конкретных условий использования защищаемого изображения. One of the ways to protect images from tampering is embedding a digital watermark –additional information destroyed by unauthorized changes. The development of digitalwatermark embedding methods that are robust against allowable transformations the mosttypical example of which is lossy compression presents a challenging task. Such methods andwatermarks embedded by them are called semi-fragile. The paper considers different semi-fragile watermarking techniques that resisting JPEG. Of particular interest is analyzing howwatermark capacity, positions of spectral coefficients selected for embedding and specificalgorithms of coefficients modification affect the quality of the resulting (secure) image. Thisstudy provides the best combinations of these parameters depending on the terms of use of aprotected image.Исследование выполнено за счет гранта Российского научного фонда (проект № 18-71-00052)