Publications

We discuss observations of C II*/C II ratios and cooling rates due to [C II] 158μm emission in high-redshift intervening damped Lyman-α (DLA) systems towards quasars. We show that the observed bimodality in the C II cooling rates actually reflects a bimodality in the C II*/C II-metallicity plane that can be naturally explained by phase segregation of the neutral medium, without invoking differences in star-formation scenarios. Assuming realistic distributions of the physical parameters to calculate the phase diagrams, we also reproduce qualitatively the metallicity dependence of this bimodality. We emphasize that high-z DLAs mostly probe low-metallicity gas (Z≲0.1Z⊙Z≲0.1Z⊙), where heating is dominated by cosmic rays (and/or turbulence), and not by photoelectric heating. Therefore, even if the gas of DLA is predominantly cold (where the cooling is dominated by [C II]), the excitation of C II can be used to derive the cosmic ray ionization rate (and/or turbulent heating), but not the UV field, as was previously considered. Alternatively, if the gas in DLA is predominantly warm, C II*/C II can be used to constrain its number density. Finally, we also discuss the importance of the ionized medium, which, if also present along the line of sight, can significantly increase the average C II*/C II ratio.

IoT devices typically stream data such as sensor values to other devices including cloud-based services. Analyzing these streams for cyber-attacks is a challenging task. This is due to the infinite nature of stream-based datatypes. Analyzing streams can require additional real-time processing and computational performance capabilities. In this article, we focus on how concept drifts affect Botnet cyber-attack detection in IoT scenarios. To reveal the result, we incorporate the concept drift analysis to detect cyber-attacks on the Bot-IoT dataset, which consists of legitimate and simulated IoT network traffics, together with various types of attacks. We designed subdatasets of the Bot-IoT to ensure the concept drift occurs that eventually complete the experiments. The detection accuracies improved 15%–26% compared with the classification models without concept drift analysis. We also gain superior performance results by comparing confusion matrices when concept drift analysis is ongoing. We propose a technique featuring a dynamic sliding window based on the residual projection to perform concept drift analysis. During the process of finding concepts in data streams, the sample number is updated dynamically by comparing the anomalous quantity obtained by the residual projection method in the current window to the previous one. In addition to the Bot-IoT dataset, our method is also applied to two popular synthetic datasets SEA Concept and UG-2C-5D. The results demonstrate the effectiveness of our method with respect to the false alarm rate, misses, and average delay.

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This editorial contains short description of a special section on data processing in distributed systems. The papers in this section are extended versions of conference papers from ADBIS 2020/

We present the discovery of neutral gas detected in both damped Lyα absorption (DLA) and H I 21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an H I bridge connecting two interacting dwarf galaxies (log (M star/M ⊙) = 8.5 ± 0.2) that host a z = 0.026 DLA with log[N(H I)/cm-2] = 20.60 ± 0.05 toward the QSO J2339-5523 (z QSO = 1.35). At impact parameters of d = 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≍0.05L * within at least Δv = ±300 km s-1 and d ≍ 350 kpc. The H I 21 cm emission is spatially coincident with the DLA at the 2σ-3σ level per spectral channel over several adjacent beams. However, H I 21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratio T s /f c > 1880 K). Observations with VLT-MUSE demonstrate that the α-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≍10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf-dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and H I 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

We consider the Dirac operator with a periodic potential on the half-line with the Dirichlet boundary condition at zero. Its spectrum consists of an absolutely continuous part plus at most one eigenvalue in each open gap. The resolvent admits a meromorphic continuation onto a two-sheeted Riemann surface with a unique simple pole on each open gap: on the first sheet (an eigenvalue) or on the second sheet (a resonance). These poles are called levels and there are no other poles. If the potential is shifted by real parameter t, then the continuous spectrum does not change but the levels can change their positions. We prove that each level is smooth and in general, non-monotonic function of t. We prove that a level is a strictly monotone function of t for a specific potential. Using these results, we obtain formulas to recover potentials of special forms.

The small-signal amplitude modulation, threshold, and spectral characteristics of microdisk lasers with InGaAs/GaAs quantum well-dots active region were studied jointly with the spectral and threshold parameters of edge-emitting lasers made from the same epitaxial heterostructure. Using the obtained material parameters, the relative intensity noise of the microdisk lasers was calculated as a function of the bias current and side-mode suppression ratio. It is shown that the integral noise is low enough for error-free optical data transmission with the maximum possible bitrate limited by the microdisk modulation bandwidth, if the bias current is above 1.7× threshold current (for side mode suppression ratio > 20 dB).

We present a spectroscopic investigation with the Very Large Telescope/X-shooter of seven candidate extremely strong damped Lyman-α absorption systems [ESDLAs, N(H I) ≥ 5 × 1021 cm-2] observed along quasar sightlines. We confirm the extremely high column densities, albeit slightly (0.1 dex) lower than the original ESDLA definition for four systems. We measured low-ionization metal abundances and dust extinction for all systems. For two systems, we also found strong associated H22 absorption logN(H2)(cm−2)=18.16±0.03log⁡N(H2)(cm−2)=18.16±0.03 and 19.28 ± 0.06 at z = 3.26 and 2.25 towards J2205+1021 and J2359+1354, respectively, while for the remaining five we measured conservative upper limits on the H22 column densities of typically logN(H2)(cm−2)<17.3log⁡N(H2)(cm−2)<17.3. The increased H2 detection rate (10-55 per cent at 68 per cent confidence level) at high H I column density compared with the overall damped Lyman-α population (~5-10 per cent) confirms previous works. We find that these seven ESDLAs have similar observed properties as those previously studied towards quasars and γ-ray burst afterglows, suggesting they probe inner regions of galaxies. We use the abundance of ionized carbon at the excited fine-structure level to calculate the cooling rates through the C II λ158 μm emission, and compare them with the cooling rates from damped Lyman-α systems in the literature. We find that the cooling rate distribution of ESDLAs also presents the same bimodality as previously observed for the general (mostly lower H I column density) damped Lyman-α population.

International news plays an important role in shaping public opinion about the foreign policy and leadership of a country. Yet research shows that the bias in favor of the current political leadership is prevalent in foreign news coverage. In this study, we explore whether these assumptions hold in the case of digital news outlets in media systems outside of established democracies. We examine the representations of Russia in digital news streams of Kazakhstan and Ukraine based on a collection of news published by about 30 top news websites in each of the countries during 2018 (n = 2,339,583 news items). To study the coverage of Russia, we follow an approach combining topic modeling for extraction of news agendas and qualitative analysis of news framing. Then, we compare Kazakhstani and Ukrainian news agendas and their framing. The results suggest that digital news media in the selected cases follow expectations based on the research of offline media despite the transformations that happened in news production with the advance of the Internet.

A simple mean-field description of frustrated antiferromagnets on hexagonal lattices, aimed to describe the high-temperature part of the temperature-magnetic field phase diagram, is proposed. It is shown that an interplay between modulation vector symmetry, Zeeman energy, and magnetodipolar interaction leads to stabilization of the triple-Q skyrmion lattice in a certain region of the phase diagram. The corresponding analytical expressions for phase boundaries are derived. The possible relevance to the high-temperature part of the Gd2PdSi3 phase diagram is discussed.

Characteristics of a compact III–V optocoupler heterogeneously integrated on a silicon substrate and formed by a 31 μm in diameter microdisk (MD) laser with a closely-spaced 50 μm × 200 μm waveguide photodetector are presented. Both optoelectronic devices were fabricated from the epitaxial heterostroctructures with InGaAs/GaAs quantum well-dot layers. The measured dark current density of the photodetector was as low as 2.1 μA cm−2. The maximum link efficiency determined as the ratio of the photodiode photocurrent increment to the increment of the microlaser bias current was 1%–1.4%. The developed heterogeneous integration of III–V devices to silicon boards by Au-Au thermocompression bonding is useful for avoiding the difficulties associated with III–V epitaxial growth on Si and facilitates integration of several devices with different active layers and waveguides. The application of MD lasers with their lateral light output is promising for simplifying requirements for optical loss at III–V/Si interface.

The low-temperature impurity-assisted photoconductivity and absorption spectra of a nanostructure with acceptor-doped multiple GaAs/AlGaAs quantum wells are investigated. The experimental absorption and photoconductivity spectra agree well with each other. Using the calculated energy spectrum of the hole and acceptor states in the quantum wells, the contributions of the transitions of holes from the ground acceptor state to the delocalized states of valence subbands and excited impurity states, and the contributions of the acceptor photoionization to the states above a quantum well, are identified.

The Schrödinger operator — Δ +V(x,y) is considered in a cylinder (Formula presented)x U, whereU is a bounded domain in (Formula presented). The spectrum of such an operator is studied under the assumption that the potential decreases in longitudinal variables, |V(x,y)| < C(x) — p. If p > 1, then the wave operators exist and are complete; the Birman invariance principle and the limiting absorption principle hold true; the absolute continuous spectrum fills the semiaxis; the singular continuous spectrum is empty; the eigenvalues can accumulate to the thresholds only. © 2022. All Rights Reserved.

For n-person multicriteria game with chance moves in extensive form, we prove the existence of pure strategy subgame perfect Pareto equilibrium (SPPE). Then we provide and demonstrate an algorithm which allows to reasonably select and construct a unique SPPE.

Program logics and semantics tell a pleasant story about sequential composition: when executing (S1;S2), we first execute S1 then S2. To improve performance, however, processors execute instructions out of order, and compilers reorder programs even more dramatically. By design, single-threaded systems cannot observe these reorderings; however, multiple-threaded systems can, making the story considerably less pleasant. A formal attempt to understand the resulting mess is known as a “relaxed memory model.” Prior models either fail to address sequential composition directly, or overly restrict processors and compilers, or permit nonsense thin-air behaviors which are unobservable in practice.

To support sequential composition while targeting modern hardware, we enrich the standard event-based approach with preconditions and families of predicate transformers. When calculating the meaning of (S1; S2), the predicate transformer applied to the precondition of an event e from S2 is chosen based on the set of events in S1 upon which e depends. We apply this approach to two existing memory models.

We  consider  Schrödinger  operators  with  periodic  potentials  on  periodic  discrete graphs.  Their  spectrum  consists  of  a  finite  number  of  bands.  We  determine  trace formulas  for  the  Schrödinger  operators.  The  proof  is  based  on  the  decomposition  of the  Schrödinger  operators  into  a  direct  integral  and  a  specific  representation  of  fiber operators.  The  traces  of  the  fiber  operators  are  expressed  as  finite  Fourier  series  of the  quasimomentum.  The  coefficients  of  the  Fourier  series  are  given  in  terms  of  the potentials  and  cycles  in  the  quotient  graph  from  some  specific  cycle  sets.  We  also present  the  trace  formulas  for  the  heat  kernel  and  the  resolvent  of  the  Schrödinger operators  and  the  determinant  formulas.

Stochastic parameters are introduced into a model of network games with production and knowledge externalities. The model was formulated by V. Matveenko and A. Korolev and generalizes Romer’s two-period model. The agents’ productivities have both deterministic and Wiener components. The research represents the dynamics of a single agent and the dynamics in a triangle that occurs in the process of combining the agents. Explicit expressions for the dynamics of a single agent and dyad agents are obtained in the form of Brownian random processes. Solutions of stochastic equations and systems are analyzed qualitatively.

In this paper, stochastic parameters are introduced into the network games model with production and knowledge’s externalities. This model was formulated by V. Matveenko and A. Korolev and generalized two-period Romer model. Agents’ productivities have deterministic and Wiener components. We consider the dynamics that occur when two complete networks are combined. Explicit expressions in the form of Brownian random processes are obtained. A qualitative analysis of the solution of a system of stochastic equations is carried out.

Big Data refers to the highly growing digital data collections that involve data with different formats, including structured, semi-structured, and unstructured datasets. Analyzing these combinations requires capabilities beyond the traditional database management systems' abilities. Among most sources of big data appears e-markets and social media platforms as significant contributors. This distinction is due to its features that facilitate consumers to express their views or opinions about specific products and services. Customer reviews and ratings become a significant resource for both consumers and firms regarding their plentiful and valuable knowledge. The proposed work introduces a big data framework to analyze such reviews and ratings, starting with data collection from different sources. Followed by integrating the collected data, which comes in different formats, toward the further processing phase. Finally, the analysis and visualization steps to draw the conclusions. Our work was tested on real data collected from active web resources.

Hierarchical topic modeling is a potentially powerful instrument for determining topical structures of text collections that additionally allows constructing a hierarchy representing the levels of topic abstractness. However, parameter optimization in hierarchical models, which includes finding an appropriate number of topics at each level of hierarchy, remains a challenging task. In this paper, we propose an approach based on Renyi entropy as a partial solution to the above problem. First, we introduce a Renyi entropy-based metric of quality for hierarchical models. Second, we propose a practical approach to obtaining the “correct” number of topics in hierarchical topic models and show how model hyperparameters should be tuned for that purpose. We test this approach on the datasets with the known number of topics, as determined by the human mark-up, three of these datasets being in the English language and one in Russian. In the numerical experiments, we consider three different hierarchical models: hierarchical latent Dirichlet allocation model (hLDA), hierarchical Pachinko allocation model (hPAM), and hierarchical additive regularization of topic models (hARTM). We demonstrate that the hLDA model possesses a significant level of instability and, moreover, the derived numbers of topics are far from the true numbers for the labeled datasets. For the hPAM model, the Renyi entropy approach allows determining only one level of the data structure. For hARTM model, the proposed approach allows us to estimate the number of topics for two levels of hierarchy.

Signed networks form a particular class of complex networks that has many applications in sociology, recommender and voting systems. The contribution of this paper is twofold. First, we propose an approach aimed at determining the characteristic subgraphs of the network. Second, we apply the developed approach to the analysis of the network describing the Wikipedia adminship elections. It is shown that this network agrees with the status theory if one does not consider strongly tied vertices, i.e., the vertices that are connected in both directions. At the same time, the strongly connected vertices mostly agree with the structural balance theory. This result indicates that there is a substantial difference between single and double connections, the fact that deserves a detailed analysis within a broader context of directed signed networks.

Now a day’s cloud-based instant message services are becoming popular. It can be an efficient way of communication even for events that require a certain level of security like banking, e-commerce applications, e-transactions etc. Cloud can provide a distributed notification of messages along with the queuing them to facilitate the transfer of messages between various applications and connected systems. Cloud message services can be as simple as a pay-as-you-go service, which does not require significant investment and protect its customers, providing a hassle-free and maintenance-free services platform. This research paper proposes a privacy-preserving approach to users utilizing cloud-based services. A cloud-based model is created and simulated. The proposed method is based on a multi-method approach where a virtual system is acting as an agent and is interconnected with other virtual systems. Inside a virtual system, a discrete event model of job processing and privacy preserving is defined as shown in the process flowchart. The proposed model is scalable. To preserve the privacy, Blowfish and Honey Encryption algorithm is used. This research aims to make the current messaging framework more secure, resilient and effective by the application of symmetric-key algorithm amalgamated with Honey key encryption. The performance of the proposed algorithm evaluated and found satisfactory results