К вопросу использования «полезных» задач для обеспечения работой блокчейн систем

This paper is a logical continuation of the paper about possible approaches to solving the “Useful Proof-of-work for blockchains” problem. We suggest some alternative ways for searching useful tasks for Proof-of-work systems. These ways are based on the process of the multiple and independent repetition of a simple experiment. The experiment is to chose an element independently and uniformly from a quite large set and then to check if the chosen element has a specific rare property. In the classic blockchain of Bitcoin this experiment is a so-called hash-puzzle. In these terms the process of solving a hash-puzzle may be replaced by searching rare astronomical objects or Go positions with specific conditions. Moreover, we describe a possible attack on the blockchain systems in which the task instance generation algorithm is replaced by the algorithm of selecting the task instance from the existing database with public access for publication of task instances and discuss the way of protection.Статья является продолжением работы о возможных подходах к решению задачи «UsefulProof-of-workforblockchains». Мы предлагаем некоторые альтернативные направления поиска полезных задач для обеспечения работой, основанные на том, что процесс решения хеш-головоломки близок к многократному независимому повторению следующего эксперимента: пусть задано достаточно большое по мощности множество (например, состоящее из 2" элементов, для достаточно большого п), только незначительная часть элементов которого обладает определенным свойством. Эксперимент состоит в равномерном выборе элемента из этого множества с последующей проверкой наличия у него указанного свойства. Таким образом, процесс решения хеш-головоломки может быть заменен, например, поиском редких астрономических объектов или поиском позиций игры Го, удовлетворяющих определенным условиям. Кроме того, мы описываем возможную атаку на блокчейн-систему, в которой алгоритм генерации индивидуальных представителей задач для обеспечения работой заменен алгоритмом выбора индивидуальных представителей из имеющейся базы данных, со стороны недобросовестных поставщиков индивидуальных представителей задач, в случае их публичного сбора, и обсуждаем некоторые способы защиты от этой атаки

Comparison between optical and electrical data on hole concentration in zinc-doped p-GaAs

The optical and electrical properties of zinc-doped Cz p-GaAs have been studied. Reflection spectra of ten p-GaAs specimens have been taken in the mid-IR region. Van der Pau galvanomagnetic, electrical resistivity and Hall coefficient measurements have been carried out for the same specimens (all the measurements were carried out at room temperature). The reflection spectra have been processed using the Kramers–Kronig relations, spectral dependences of the real and imaginary parts of the complex dielectric permeability have been calculated and loss function curves have been plotted. The loss function maximum position has been used to calculate the characteristic wavenumber corresponding to the high-frequency plasmon-phonon mode frequency. Theoretical calculations have been conducted and a calibration curve has been built up for determining heavy hole concentration in p-GaAs at T = 295 K based on known characteristic wavenumber. Further matching of the optical and Hall data has been used for determining the light to heavy hole mobility ratio. This ratio proves to be in the 1.9–2.8 range which is far lower as compared with theoretical predictions in the assumption of the same scattering mechanism for light and heavy holes (at optical phonons). It has been hypothesized that the scattering mechanisms for light and heavy holes differ

On the Issue of Using “Useful” Tasks for Proof of Works in Blockchain

This paper is a logical continuation of the paper about possible approaches to solving the “Useful Proof-of-work for blockchains” problem. We suggest some alternative ways for searching useful tasks for Proof-of-work systems. These ways are based on the process of the multiple and independent repetition of a simple experiment. The experiment is to chose an element independently and uniformly from a quite large set and then to check if the chosen element has a specific rare property. In the classic blockchain of Bitcoin this experiment is a so-called hash-puzzle. In these terms the process of solving a hash-puzzle may be replaced by searching rare astronomical objects or Go positions with specific conditions. Moreover, we describe a possible attack on the blockchain systems in which the task instance generation algorithm is replaced by the algorithm of selecting the task instance from the existing database with public access for publication of task instances and discuss the way of protection

Comparison between optical and electrophysical data on free electron concentration in tellurium doped n-GaAs

A theoretical model has been developed for determining free electron concentration in n-GaAs from characteristic points in the far infrared region of reflection spectra. We show that when determining free electron concentration one should take into account the pasmon–phonon coupling, otherwise free electron concentration will be overestimated. We have calculated electron concentration Nopt as a function of characteristic wave number ν+ which is described by a second order polynomial. Twenty-five tellurium doped gallium arsenide specimens have been tested for electron concentration using two methods, i.e., the conventional four-probe method (Van der Pau) and the optical method developed by us (the measurements have been carried out at room temperature). We have used the experimental results to plot the dependence of electron concentration based on the Hall data (NHall) on electron concentration based on the optical data (Nopt). This dependence is described by a linear function. We show that the data of optical and electrophysical measurements agree if the electron concentration is Neq = 1.07 · 1018 cm-3. At lower Hall electron concentrations, NHall Nopt. We have suggested a qualitative model describing these results. We assume that tellurium atoms associate into complexes with arsenic vacancies thus reducing the concentration of electrons. The concentration of arsenic vacancies is lower on the crystal surface, hence the Nopt > NHall condition should be met. With an increase in doping level, more and more tellurium atoms remain electrically active, so the bulk concentration of electrons starts to prevail over the surface one. However with further increase in doping level the NHall/Nopt ratio starts to decrease again and tends to unity. This seems to originate from the fact that the decomposition intensity of the tellurium atom + arsenic vacancy complexes decreases with an increase in doping level

Comparison between results of optical and electrical measurements of free electron concentration in n-InAs specimens

A theoretical model has been developed for determining the free electron concentration in n-InAs specimens from characteristic points in far IR reflection spectra. We show that this determination requires plasmon-phonon coupling be taken into account, otherwise the measured electron concentration proves to be overestimated. A correlation between the electron concentration Nopt and the characteristic wavenumber ν+ has been calculated and proves to be well fit by a third order polynomial. The test specimens have been obtained by tin or sulfur doping of indium arsenide. The electron concentration in the specimens has been measured at room temperature using two methods: the optical method developed by the Authors (Nopt) and the conventional four-probe Hall method (the Van der Pau method, NHall). The reflecting surfaces of the specimens have been chemically polished or fine abrasive ground. The condition Nopt > NHall has been shown to hold for all the test specimens. The difference between the optical and the Hall electron concentrations is greater for specimens having polished reflecting surfaces. The experimental data have been compared with earlier data for n-GaAs. A qualitative model explaining the experimental data has been suggested

Comparison between optical and electrical data on hole concentration in zinc-doped p-GaAs

The optical and electrical properties of zinc-doped Cz p-GaAs have been studied. Reflection spectra of ten p-GaAs specimens have been taken in the mid-IR region. Van der Pau galvanomagnetic, electrical resistivity and Hall coefficient measurements have been carried out for the same specimens (all the measurements were carried out at room temperature). The reflection spectra have been processed using the Kramers–Kronig relations, spectral dependences of the real and imaginary parts of the complex dielectric permeability have been calculated and loss function curves have been plotted. The loss function maximum position has been used to calculate the characteristic wavenumber corresponding to the high-frequency plasmon-phonon mode frequency. Theoretical calculations have been conducted and a calibration curve has been built up for determining heavy hole concentration in p-GaAs at T = 295 K based on known characteristic wavenumber. Further matching of the optical and Hall data has been used for determining the light to heavy hole mobility ratio. This ratio proves to be in the 1.9–2.8 range which is far lower as compared with theoretical predictions in the assumption of the same scattering mechanism for light and heavy holes (at optical phonons). It has been hypothesized that the scattering mechanisms for light and heavy holes differ

Identification of natural hybrids between Ahlbergia frivaldszkyi (Lederer, 1853) and Callophrys rubi (Linnaeus, 1758) (Lepidoptera, Lycaenidae) using mitochondrial and nuclear markers

Natural hybridization is rather widespread and common in animals and can have important evolutionary consequences. In terms of taxonomy, exploring hybridization and introgression is crucial in defining species boundaries and testing taxonomic hypotheses. In the present paper, we report on natural hybrid specimens between Ahlbergia frivaldszkyi (Lederer, 1853) and Callophrys rubi (Linnaeus, 1758). To test the hypothesis of their hybrid origin, we employed the molecular mitochondrial (COI gene) and nuclear (wingless, RPS5, and Ca-ATPase genes) markers commonly used in phylogenetic studies and explored the morphology of the specimens. Our analysis revealed that hybrids bear mitochondrial haplotypes of C. rubi, while nuclear fragments are heterozygous, sharing a combination of A. frivaldszkyi and C. rubi lineages. The hybrid specimens combine morphological characters of both genera. Our results for the first time empirically demonstrate the possibility of genetic introgression between these species and between the genera Callophrys and Ahlbergia on the whole

First terahertz-range experiments on pump – probe setup at Novosibirsk free electron laser

A single-color pump-probe system has been commissioned at the Novosibirsk free electron laser. The laser emits a tunable monochromatic terahertz radiation. To prove the proper system operation, we investigated the time-resolved absorption of a sample of n-type germanium doped with antimony, which was previously investigated at the FELBE facility, in the temperature range from 5 to 40 K. The measured relaxation time amounted to about 1.7 ns, which agreed with the results obtained at the FELBE. The results of pump-probe measurements of non-equilibrium dynamics of hot electrons in the germanium crystal at cryogenic temperatures are presented for wavelengths of 105, 141 and 150 μm

Composition, Structure and Reduction Reactivity of Composite Materials of the α-Fe₂O₃–СaFe₂O₄ System by Hydrogen

В работе изучены композиционные материалы системы α-Fe2O3–CaFe2O4, полученные методом высокотемпературного твердофазного синтеза из оксидов Са и Fe(III) с вариацией мольного отношения СаО/Fe2O3 от 0.15 до 1.00. Материалы охарактеризованы методами рентгеновской дифракции (РФА), сканирующей электронной микроскопии с системой энергодисперсионного микроанализа (СЭМ-ЭДС) и синхронного термического анализа (СТА) в режиме термопрограммируемого восстановления водородом (H2-ТПВ). СЭМ-ЭДС – исследование образцов выявило формирование сложной микроструктуры материала по типу «ядро-оболочка» с фазой гематита в качестве «ядра». H2-ТПВ образцов позволило установить, что с увеличением содержания фазы CaFe2O4 (от 33.4 до 97.5 мас. %) наблюдается снижение вклада низкотемпературных форм решеточного кислорода в областях 350-510 °С (до 2.6 раза) и 510-650 °С (до 1.7 раза) и рост вклада высокотемпературной формы кислорода в интервале 650-900 °С (до 2 раз). На основе оценки подвижности решеточного кислорода высказано предположение о перспективности использования полученных композиционных материалов с содержанием фазы CaFe2O4 более 55.2 мас. % в качестве носителей кислорода в химических циклических процессах получения синтез-газаIn this paper, α-Fe2O3–CaFe2O4 composite materials obtained by high-temperature solid-phase synthesis from Ca and Fe (III) oxides with varying molar ratio CaO/Fe2O3 in the range 0.15-1.00 were investigated. The materials are characterized by Х-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS) and simultaneous thermal analysis (STA) in the hydrogen temperature-programmed reduction mode (H2-TPR). SEM-EDS studies of the specimens were revealed a formation of the “core-shell” type complex microstructure of material with the hematite phase as the “core”. H2-TPR of the specimens allowed to establish a decrease of the contribution of low-temperature forms of lattice oxygen in areas of 350-510 °С (up to 2.6 times) and 510-650 °С (up to 1.7 times), and the growth of the contribution of the high-temperature oxygen form in the range of 650-900 °С (up to 2 times) with an increase in the content of the phase CaFe2O4 from 33.4 to 97.5 wt. %. Relying on the assessment of lattice oxygen mobility, it was suggested, that the samples with content of CaFe2O4 phase more than 55.4 wt. % are promising for use as oxygen carriers in chemical looping processes of syngas productio