Skeletally Dugundji spaces

We introduce and investigate the class of skeletally Dugundji spaces as a skeletal analogue of Dugundji space. The main result states that the following conditions are equivalent for a given space $X$: (i) $X$ is skeletally Dugundji; (ii) Every compactification of $X$ is co-absolute to a Dugundji space; (iii) Every $C^*$-embedding of the absolute $p(X)$ in another space is strongly $\pi$-regular; (iv) $X$ has a multiplicative lattice in the sense of Shchepin \cite{s76} consisting of skeletal maps

On generalized VnV^n-continua

The notion of $V^n$-continua was introduced by Alexandroff \cite{ps} as a generalization of the concept of $n$-manifold. In this note we consider the cohomological analogue of $V^n$-continua and prove that any strongly locally homogeneous, generalized continuum $X$ with cohomological dimension $n$ is a generalized $V^n$-con\-ti\-nuum with respect to the cohomological dimension. In particular, every strongly locally homogeneous continuum of covering dimension $n$ is a $V^n$-continuum in the sense of Alexandroff. An analog of the Mazurkiewicz theorem that no subset of covering dimension $\le n-2$ cuts any region of the Euclidean $n$-space is also obtained for strongly locally homogeneous, generalized continua of cohomological dimension $n$.Comment: 7 page

Standards for the Characterization of Endurance in Resistive Switching Devices

Resistive switching (RS) devices are emerging electronic components that could have applications in multiple types of integrated circuits, including electronic memories, true random number generators, radiofrequency switches, neuromorphic vision sensors, and artificial neural networks. The main factor hindering the massive employment of RS devices in commercial circuits is related to variability and reliability issues, which are usually evaluated through switching endurance tests. However, we note that most studies that claimed high endurances >106 cycles were based on resistance versus cycle plots that contain very few data points (in many cases even <20), and which are collected in only one device. We recommend not to use such a characterization method because it is highly inaccurate and unreliable (i.e., it cannot reliably demonstrate that the device effectively switches in every cycle and it ignores cycle-to-cycle and device-to-device variability). This has created a blurry vision of the real performance of RS devices and in many cases has exaggerated their potential. This article proposes and describes a method for the correct characterization of switching endurance in RS devices; this method aims to construct endurance plots showing one data point per cycle and resistive state and combine data from multiple devices. Adopting this recommended method should result in more reliable literature in the field of RS technologies, which should accelerate their integration in commercial products

Interactive models of communication at the nanoscale using nanoparticles that talk to one another

[EN] 'Communication' between abiotic nanoscale chemical systems is an almost-unexplored field with enormous potential. Here we show the design and preparation of a chemical communication system based on enzyme-powered Janus nanoparticles, which mimics an interactive model of communication. Cargo delivery from one nanoparticle is governed by the biunivocal communication with another nanoparticle, which involves two enzymatic processes and the interchange of chemical messengers. The conceptual idea of establishing communication between nanodevices opens the opportunity to develop complex nanoscale systems capable of sharing information and cooperating.A. L.-L. is grateful to 'La Caixa' Banking Foundation for his PhD fellowship. We wish to thank the Spanish Government (MINECO Projects MAT2015-64139-C4-1, CTQ2014-58989-P and CTQ2015-71936-REDT and AGL2015-70235-C2-2-R) and the Generalitat Valenciana (Project PROMETEOII/2014/047) for support. 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Comparative characterization of different variants of quantitative chromatographic analysis using external and internal standards

Хроматографический анализ серии характеризуемых и градуировочных двухкомпонентных образцов (растворы аналита и стандарта) позволяет сопоставить возможности и особенности одновременно шести вариантов количественных определений способами внешнего и внутреннего стандарта по критериям точности результатов (значениям случайных и систематических погрешностей). Они включают простейший вариант способа внешнего стандарта (I), модифицированный вариант, предполагающий использование дополнительного стандарта и усреднение не абсолютных, а относительных площадей пиков (II), обычно используемый способ внутреннего стандарта (III) и его модифицированную аналогичным образом версию (IV). Кроме этого рассмотрены два варианта использования гомолога аналита в качестве внутреннего стандарта без учета градуировочных коэффициентов (V) и (VI). Это представляет интерес для оптимизации практических работ по хроматографии и процесса обучения предмету. Требования к дополнительным и внутренним стандартам не идентичны. В качестве дополнительных стандартов можно выбирать любые соединения, как введенные в образцы искусственно, так и уже присутствующие в них, причем точное задание их концентраций не требуется. Необходимо лишь обеспечить их равенство в характеризуемом и градуировочном растворах. Показано, что модифицированные варианты методов внешнего и внутреннего стандартов характеризуются одинаковыми относительными стандартными отклонениями результатов. Показано, что минимальными случайными составляющими погрешностями характеризуются варианты, предполагающие применение дополнительного (II) или внутреннего стандарта (IV) и усреднение отношений площадей пиков целевых аналитов и таких стандартов. Для них же минимальны систематические погрешности определений. Для выявления возможных искажений состава анализируемых образцов, обусловленных частичным испарением летучих компонентов в процессе работы с такими образцами, информативен контроль значений градуировочных коэффициентов.Chromatographic analysis of a series of two-component samples (solutions of a target analyte and a standard) allows simultaneous comparison of the possibilities and features of six variants of quantitative analysis using the external and internal standards techniques according to the criteria of results precision and repeatability (random and systematic errors values). These variants include the simplest version of the external standard method (I); its modified version (II) that implies the application of an additional standard and averaging not the absolute, but relative peak areas; the commonly used version of the internal standard method (III); and its version modified in a similar manner (IV). Besides, two variants of using a homologue of the target analyte as the internal standard without determining the calibration coefficients are considered (V) and (VI). This topic is of interest for optimization of practical works on chromatography and teaching the subject in general. The requirements to the additional and internal standards are not identical. Any compound (both present in the samples or added to them) can be selected as the additional standards, and precise setting of their concentrations is not required. It is only necessary to ensure their equal concentrations in the analyzed and reference solutions. It is shown that the modified versions of the external and internal standard methods are characterized by the equal relative standard deviations of the results. The minimal relative standard deviations of the results are typical for the variants implying the use of an additional (II) or an internal (IV) standard and the averaging the ratio of peak areas of target analytes and such standards. The systematic errors of determinations appeared to be minimal for the same variants. Controlling the values of the calibration coefficients is informative for revealing the possible distortions of the composition of samples due to the partial evaporation of volatile constituents in the course of handling such samples.Практическая работа, результаты которой составили предмет настоящего сообщения, выполнена с использованием оборудования Ресурсного Центра «Методы анализа состава вещества» Санкт-Петербургского государственного университета. Авторы благодарят сотрудников Центра за содействие.The students’ work, which results are discussed in this paper, was carried out at the Center for Chemical and Material Research of St. Petersburg State University’s Research Park. The author is grateful to the staff of this Center for the assistance