bluuebunny/crossref_metadata_2025 huggingface dataset:
Innovative undergraduate education strategy
Authors: Kuznecova Viktoriya , Ivanova Marina , Starkova Elena
Published: December 2020

The article examines various methods of enhancing the undergraduate learning process efficiency through the use of the unique lesson structure based on implementing the innovative teaching techniques such as hackathon and networking allowing students to develop valuable soft skills. The main recommendations for the arrangement of these methods are described. The new types of research sessions such as excursion lessons which include a group laboratory work or research projects are studied in order to improve students’ hard skills. The distinctive features of practical discussion classes are considered as well.
Staff education resource regarded as the capital asset of a company
Authors: Kopteva Lyudmila , Ivanova Maria , Barinov Sergey
Published: December 2020

Personnel training lasts a lifetime. This is what the existing system of persistent professional education is aimed at. This system implies the possibility of continuing the education at any moment of life from the level at which a person stopped previously. In the article, the concept of continuous professional training in the context of its methodology is considered and the key features of human and education resources are discovered. The particular attention is paid to the issue of obsolescence of the staff education resource and the rationale for its diagnostics conducted through the audit of intellectual capital. The necessity of development of the educational resource for the staff of a modern company and the consequent increase of its competitiveness is presented.
Methodological aspects of the implementation of additional education in robotics
Authors: Kadeeva Oksana , Belov Alexander , Syritsyna Valentina , Maksimenko Svetlana , Sinko Viktor
Published: December 2020

The purpose of the study is actualized by the fact that progress in the field of computer technology and robotics allows radically changing the idea of teaching computer science to schoolchildren, or rather programming in a modern secondary school, realizing one of the most important tasks facing the education system today. The scientific novelty of the study lies in the fact that these achievements allow updating traditional teaching methods, making them much more useful and modern. Nowadays, students have the opportunity to study various programming languages at school and at the same time, using the developed resources, observe the process of their execution by specially created robots, which can develop the student's desire to study further and give motivation to study the academic discipline. The practical significance of the work lies in the fact that one of such projects containing educational resources and allowing a different look at modern computer science lessons is LEGO and ROBBO. The advantages and disadvantages of traditional methods of teaching programming languages in high school are analyzed in the study. Also, the advantages of learning programming with LEGO and ROBBO are revealed, methodological recommendations for using the LEGO and ROBBO programming environment are presented, the capabilities of the LEGO project and ROBBO are described, and their main elements are characterized.
A three-dimensional finite element-approach to investigate the optimum cutting parameters in machining AA2024
Authors: Ijaz Hassan , Danish Mohd , Asad Muhammad , Rubaiee Saeed
Published: December 2020

This research work presents a numerical study of the orthogonal cutting process employing a finite element approach to optimize dry machining of aluminium alloy 2024. The main objective of the research work is to perform three-dimensional finite element simulations for a better understanding of temperature distribution and residual stresses development in the workpiece and tool regions along depth of cut direction. While, two-dimensional models don't predict true picture of aforesaid parameters along cutting depth due to material's out of plane flow and deformation. In the present study, effects of tool rake angles (7°, 14°, 21°) and cutting speeds (200, 400, 800 m/min) upon variations in chip geometry at various sections along workpiece width (depth of cut) have been discussed at large. Furthermore, cutting forces and tool-workpiece temperature profiles are also in depth analysed. The findings will lead the manufacturers to better decide post machining processes like heat treatment, deburring, surface treatments, etc. The results showed that a combination of a rake angle of 14° at cutting velocity of 800 m/min produces serrated chip segments with relatively moderate cutting forces in comparison to other parametric combinations. The efficacy of the presented finite element model is verified by comparing the numerically obtained results with experimental ones.
The “diagnose and leave in” strategy for diminutive rectosigmoid polyps in Lynch syndrome: a post hoc analysis from a randomized controlled trial
Authors: Rivero-Sánchez Liseth , Gavric Aleksandar , Herrero Jesús , Remedios David , Alvarez Victoria , Albéniz Eduardo , Gordillo Jordi , Puig Ignasi , López-Vicente Jorge , Huerta Alain , López-Cerón María , Salces Inmaculada , Peñas Beatriz , Parejo Sofía , Rodriguez Enrique , Herraiz Maite , Carretero Cristina , Gimeno-Garcia Antonio Z. , Saperas Esteban , Alvarez Cristina , Arnau-Collell Coral , Ortiz Oswaldo , Sánchez Ariadna , Jung Gerhard , Balaguer Francesc , Pellisé María
Published: December 2020

Background The “diagnose-and-leave-in” policy has been established to reduce the risks and costs related to unnecessary polypectomies in the average-risk population. In individuals with Lynch syndrome, owing to accelerated carcinogenesis, the general recommendation is to remove all polyps, irrespective of size, location, and appearance. We evaluated the feasibility and safety of the diagnose-and-leave-in strategy in individuals with Lynch syndrome.

Methods We performed a post hoc analysis based on per-polyp data from a randomized, clinical trial conducted by 24 dedicated colonoscopists at 14 academic centers, in which 256 patients with confirmed Lynch syndrome underwent surveillance colonoscopy from July 2016 to January 2018. In vivo optical diagnosis with confidence level for all detected lesions was obtained before polypectomy using virtual chromoendoscopy alone or with dye-based chromoendoscopy. Primary outcome was the negative predictive value (NPV) for neoplasia of high-confidence optical diagnosis among diminutive (≤ 5 mm) rectosigmoid lesions. Histology was the reference standard.

Results Of 147 rectosigmoid lesions, 128 were diminutive. In 103 of the 128 lesions (81 %), the optical diagnostic confidence was high and showed an NPV of 96.0 % (95 % confidence interval [CI] 88.9 %–98.6 %) and accuracy of 89.3 % (95 %CI 81.9 %–93.9 %). By following the diagnose-and-leave-in policy, we would have avoided 59 % (75/128) of polypectomies at the expense of two diminutive low grade dysplastic adenomas and one diminutive sessile serrated lesion that would have been left in situ.

Conclusion In patients with Lynch syndrome, the diagnose-and-leave-in strategy for diminutive rectosigmoid polyps would be feasible and safe.
Prevalence and Neighborhood Geomapping of COVID-19 in an Underserved Chicago Pregnant Population
Authors: Buhimschi Catalin S. , Elam Gloria L. , Locher Stephen R. , Norris-Stojak Doreen , Aldasoqi Hayfaa , Stephenson Mary D. , Buhimschi Irina A.
Published: December 2020

Objective The Chicago area is known to harbor some of the deepest racial and ethnic socioeconomic inequalities in the United States. We studied the prevalence and neighborhood distribution of patients who tested positive for COVID-19 after implementation of universal screening at an academic hospital providing obstetrical services to an underserved Chicago population.

Study Design From April 16 to June 16, 2020, a total of 369 patients were screened for COVID-19 at University of Illinois at Chicago with either the Abbott Point-of-Care (POC, n = 266) or reverse transcription polymerase chain reaction test (RT-PCR, n = 101). Patient residential data mapped using ESRI ArcGIS Pro was integrated in ESRI's Living Atlas with the Neighborhood Socioeconomic Status Index (NSEI).

Results Precisely, 7.9% (29/369) of screened patients tested positive; 69% (17/29) with the POC test and 31% (12/29) by RT-PCR. The prevalence of an outpatient RT-PCR positive result was 8.9% (9/101). All but one of the 29 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positive patients were either Hispanic or Black, and the majority resided in disadvantaged neighborhoods.

Conclusion The disproportionate hit of COVID-19 pandemic on the Hispanic and Black communities reflects in SARS-CoV-2 positivity rates in the obstetrical population. Our report provides data that may be useful to policy makers when prioritizing resources to communities in need.
Dermal fibroblasts and triple-negative mammary epithelial cancer cells differentially stiffen their local matrix
Authors: Jagiełło Alicja , Lim Micah , Botvinick Elliot
Published: December 2020

The bulk measurement of extracellular matrix (ECM) stiffness is commonly used in mechanobiology. However, past studies by our group show that peri-cellular stiffness is quite heterogeneous and divergent from the bulk. We use optical tweezers active microrheology (AMR) to quantify how two phenotypically distinct migratory cell lines establish dissimilar patterns of peri-cellular stiffness. Dermal fibroblasts (DFs) and triple-negative human breast cancer cells MDA-MB-231 (MDAs) were embedded within type 1 collagen (T1C) hydrogels polymerized at two concentrations: 1.0 mg/ml and 1.5 mg/ml. We found DFs increase the local stiffness of 1.0 mg/ml T1C hydrogels but, surprisingly, do not alter the stiffness of 1.5 mg/ml T1C hydrogels. In contrast, MDAs predominantly do not stiffen T1C hydrogels as compared to cell-free controls. The results suggest that MDAs adapt to the bulk ECM stiffness, while DFs regulate local stiffness to levels they intrinsically prefer. In other experiments, cells were treated with transforming growth factor-β1 (TGF-β1), glucose, or ROCK inhibitor Y27632, which have known effects on DFs and MDAs related to migration, proliferation, and contractility. The results show that TGF-β1 alters stiffness anisotropy, while glucose increases stiffness magnitude around DFs but not MDAs and Y27632 treatment inhibits cell-mediated stiffening. Both cell lines exhibit an elongated morphology and local stiffness anisotropy, where the stiffer axis depends on the cell line, T1C concentration, and treatment. In summary, our findings demonstrate that AMR reveals otherwise masked mechanical properties such as spatial gradients and anisotropy, which are known to affect cell behavior at the macro-scale. The same properties manifest with similar magnitude around single cells.
Electric field-induced boron nitride/silver nanoparticle template discharge for fluorescence signal enhancement
Authors: Fularz Agata , Almohammed Sawsan , Rice James H.
Published: December 2020

Enabling an understanding of the optical properties of functional inorganic–organic materials is crucial for driving development in many areas such as medicine and optoelectronics. In particular the use of two-dimensional materials such as hexagonal boron nitride has been recently investigated for the fabrication of nanohybrid composites due to the unique properties of the material. Here we report the use of boron nitride/silver nanoparticle (BN/AgNP) composite templates as an effective substrate for controlling the fluorescence emission of adsorbed organic molecules through applying external electric fields in the range of 0 to 3 × 104 V/m. We report fluorescence quenching in the field and enhancement of fluorescence signal intensity of J-aggregate porphyrins up to 20 min following removal of the applied voltage. We propose that the observed enhancement can be attributed to charge release upon switching off the field due to capacitance effects associated with the BN/AgNP substrate.
Simulated tempering with irreversible Gibbs sampling techniques
Authors: Faizi Fahim , Buigues Pedro J. , Deligiannidis George , Rosta Edina
Published: December 2020

We present here two novel algorithms for simulated tempering simulations, which break the detailed balance condition (DBC) but satisfy the skewed detailed balance to ensure invariance of the target distribution. The irreversible methods we present here are based on Gibbs sampling and concern breaking DBC at the update scheme of the temperature swaps. We utilize three systems as a test bed for our methods: a Markov chain Monte Carlo simulation on a simple system described by a one-dimensional double well potential, the Ising model, and molecular dynamics simulations on alanine pentapeptide (ALA5). The relaxation times of inverse temperature, magnetic susceptibility, and energy density for the Ising model indicate clear gains in sampling efficiency over conventional Gibbs sampling techniques with DBC and also over the conventionally used simulated tempering with the Metropolis–Hastings (MH) scheme. Simulations on ALA5 with a large number of temperatures indicate distinct gains in mixing times for inverse temperature and consequently the energy of the system compared to conventional MH. With no additional computational overhead, our methods were found to be more efficient alternatives to the conventionally used simulated tempering methods with DBC. Our algorithms should be particularly advantageous in simulations of large systems with many temperature ladders, as our algorithms showed a more favorable constant scaling in Ising spin systems as compared with both reversible and irreversible MH algorithms. In future applications, our irreversible methods can also be easily tailored to utilize a given dynamical variable other than temperature to flatten rugged free energy landscapes.
Plasmon induced charge transfer mechanism in gold-TiO2 nanoparticle systems: The size effect of gold nanoparticle
Authors: Du Luchao , Shi Xiaoping , Zhang Guirong , Furube Akihiro
Published: December 2020

The application of surface plasmon in the solar-cell design has become a hot topic in the field of photovoltaic research. The enhancement of the photoelectric conversion efficiency is due to charge transfer caused by photoinduced injection of electrons from the metal to the corresponding acceptors. Revealing the basic physical mechanism further is of very important practical significance. We used the femtosecond time-resolved IR ultrafast spectroscopy technology and chose to excite the plasmon band of gold while changing the size of the gold nanoparticle to regulate the complex nanoprocess of the separation and recombination of photogenerated electrons in gold assembled with TiO2 systems. Behavior of hot holes in gold was also considered. We found that larger gold particles resulted in longer charge recombination times. The mechanism is discussed in detail in terms of restricted carrier diffusion in the nanospace.
H/D isotope effect observed in the isotropic Fermi contact interaction of formyl radical: Experimental and theoretical analysis of the inter- and intra-molecular dynamics
Authors: Dmitriev Yurij A. , Laaksonen Aatto , Benetis Nikolas P.
Published: December 2020

An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions.
Electrohydrodynamics of a droplet in a highly confined domain: A numerical study
Authors: Saghatchi Roozbeh , Rahmat Amin , Yildiz Mehmet
Published: December 2020

In this paper, electrohydrodynamics (EHD) deformation of a droplet in a highly confined domain is studied by using the incompressible smoothed particle hydrodynamics method. Simulations are performed for six different systems of a droplet and ambient fluid corresponding to different electrical properties. The effects of confinement ratios, from 0 to 0.95, on the droplet deformation are discussed thoroughly. It is shown that the deformation is highly dependent on the ratios of electrical permittivity, electrical conductivity, and confinement ratio. To demonstrate the droplet behavior, electric force components on the droplet interface are calculated and discussed in detail. It is shown that the interaction of these forces plays a major role in the droplet deformation. Furthermore, it is illustrated that the pressure force becomes significant at high confinement ratios and affects the droplet behavior in addition to the electric forces. Different values of unbounded deformation are selected for the EHD simulation. The effect of unbounded deformation on the droplet behavior is also discussed, and it is found that the unbounded deformation influence is important in some of the systems and confinement ratios.
Acoustic streaming in second-order fluids
Authors: Das Pradipta Kr. , Snider Arthur David , Bhethanabotla Venkat R.
Published: December 2020

In this article, inner acoustic streaming for second-order fluids has been studied analytically by employing asymptotic expansions for a thin Stokes layer and low acoustic Mach number. In addition, a multiple-timescale approach has been adopted to separate the primary oscillatory flow and the steady acoustic streaming. The study considers two sample cases: (i) motionless boundary and (ii) vibrating boundary and compares the characteristics associated with their streaming. It is observed that both the primary oscillatory flow and acoustic streaming flow fields are suppressed in second-order fluids due to the extra stress components present in the fluids. This study considers both compressible and incompressible Stokes layers to bring out the acoustic streaming characteristics associated with fluid compressibility. For the compressible Stokes layer, stronger acoustic streaming flow results for the motionless boundary, leveraging the deeper interaction between the primary oscillatory pressure field and the steady streaming. In the case of a vibrating boundary, the primary oscillatory pressure field is independent of the Stokes layer compressibility, and hence, the acoustic streaming flow remains unaltered. The extra stresses in second-order fluids reduce the acoustic body force density, and the maximum reduction has been observed for the vibrating boundary. In order to understand Lagrangian streaming, Stokes drift has also been calculated and compared for all the scenarios. The theoretical analysis and fundamental insights derived from this study have potential for applications in diverse fields such as particle manipulation, biosensing, cell sorting, and removal of loosely bound material such as non-specifically bound proteins.
Dynamic flow resistivity and sound absorption of compressed fibrous porous materials: Experimental and theoretical
Authors: Ning Jingfeng , Li Yueming
Published: December 2020

Fibrous porous materials are the preferred absorbers for many applications since they can absorb impact energy and sound waves. The microscopic morphology and the relationship between the compressed state and sound absorption characteristics are studied for compressed fibrous porous materials. A series of specimens of fibrous porous materials are prepared and compressed to different thicknesses, and their pore size distributions are analyzed. The average pore size, dynamic flow resistivity, and acoustic impedance of the compressed fibrous porous materials are derived theoretically. The effects of porosity, thickness, average pore size, compression ratio, and combinations of these parameters on the dynamic flow resistivity and sound absorption coefficient of compressed fibrous porous materials are discussed theoretically. It is demonstrated that the compression ratio decreases the sound absorption coefficient of fibrous porous materials. The compression ratio and average pore size are important factors for the dynamic flow resistivity and sound absorption coefficient. Our results could help establish a theoretical foundation for understanding the microscopic morphology of compressed fibrous porous materials and aid the design of fibrous porous materials for various applications.
Axial distributions of bubble–liquid mass transfer coefficient in laboratory-scale stirred tank with viscous Newtonian and non-Newtonian fluids
Authors: Ali Haider , Solsvik Jannike
Published: December 2020

Splitting of the volumetric mass transfer coefficient into a bubble–liquid mass transfer coefficient and interfacial area is essential to quantify the mass transfer rate of stirred tanks precisely. Axial distributions of the bubble–liquid mass transfer coefficient were determined in viscous Newtonian and non-Newtonian fluids using a laboratory-scale stirred tank. A detailed knowledge of the bubble–liquid mass transfer coefficient was obtained by using dedicated in situ oxygen and bubble size endoscope probes simultaneously. The volumetric mass transfer coefficient was estimated from recorded local dissolved oxygen concentrations in liquids. The interfacial area was calculated by measuring the bubble size and gas hold-up. The bubble–liquid mass transfer coefficient was then obtained by combining the estimated volumetric mass transfer coefficient and interfacial area. The bubble–liquid mass transfer coefficient was evaluated with effects of fluid rheology (concentrations of fluids), operating conditions (power input and superficial gas velocity), and axial liquid height. Bubble breakage is higher close to the stirrer due to intensive turbulence. The bubble–liquid mass transfer coefficient depended directly on operating conditions and indirectly on fluid rheology and liquid height.
Anisotropy and anharmonicity in polystyrene stable glass
Authors: Raegen Adam N. , Zhou Qi , Forrest James A.
Published: December 2020

We have used ellipsometry to characterize the anisotropy in stable polymer glasses prepared by physical vapor deposition. These measurements reveal birefringence values (as measured by the magnitude of in-plane vs out-of-plane refractive index) less than 0.002 in vapor-deposited polystyrenes with N from 6 to 12 and with fictive temperatures between 10 K and 35 K below the Tg values. We have measured the thermal expansivity of these stable glasses and compared to ordinary rejuvenated glass. The thermal expansivity of the stable glasses is less than that of ordinary glass with a difference that increases as the fictive temperature Tf decreases.
Directionality of light absorption and emission in representative fluorescent proteins
Authors: Myšková Jitka , Rybakova Olga , Brynda Jiří , Khoroshyy Petro , Bondar Alexey , Lazar Josef
Published: December 2020

Significance

Fluorescent proteins have been used extensively in many areas of life sciences. Many of their applications rely on their various biophysical properties, such as excitation and emission wavelengths, excited state lifetimes, or sensitivity to the molecular environment. One aspect of fluorescent proteins that has remained largely neglected is the directionality of their optical properties. In the present work, we describe our experimental determination of the directionality of light absorption and emission in several commonly used fluorescent proteins. Our findings improve our understanding of fundamental properties of fluorescent proteins, and expand the possibilities of development and applications of genetically encoded fluorescent probes.
How operationalizations of word types affect measures of lexical diversity
Authors: Jarvis Scott , Hashimoto Brett James
Published: December 2020

This study tests three measures of lexical diversity (LD), each using five operationalizations of word types. The measures include MTLD (measure of textual lexical diversity), MTLD-W (moving average MTLD with wrap-around measurement), and MATTR (moving average type-token ratio). Each of these measures is tested with types operationalized as orthographic forms, lemmas using automated POS tags, lemmas using manually corrected POS tags, flemmas (list-based lemmas that do not distinguish between parts of speech), and word families. These measures are applied to 60 narrative texts written in English by adolescent native speakers of English (n = 13), Finnish (n = 31), and Swedish (n = 16). Each individual LD measure is evaluated in relation to how well it correlates with the mean LD ratings of 55 human raters whose inter-rater reliability was exceedingly high (Cronbach’s alpha = .980). The overall results show that the three measures are comparable but two of the operationalizations of types produce mixed results across measures.
Improve the performance of interferometer with ultra-cold atoms*
Authors: Dong Xiangyu , Jin Shengjie , Shui Hongmian , Peng Peng , Zhou Xiaoji
Published: December 2020

Ultra-cold atoms provide ideal platforms for interferometry. The macroscopic matter-wave property of ultra-cold atoms leads to large coherent length and long coherent time, which enable high accuracy and sensitivity to measurement. Here, we review our efforts to improve the performance of the interferometer. We demonstrate a shortcut method for manipulating ultra-cold atoms in an optical lattice. Compared with traditional ones, this shortcut method can reduce the manipulation time by up to three orders of magnitude. We construct a matter-wave Ramsey interferometer for trapped motional quantum states and significantly increase its coherence time by one order of magnitude with an echo technique based on this method. Efforts have also been made to enhance the resolution by multimode scheme. Application of a noise-resilient multi-component interferometer shows that increasing the number of paths could sharpen the peaks in the time-domain interference fringes, which leads to a resolution nearly twice compared with that of a conventional double-path two-mode interferometer. With the shortcut method mentioned above, improvement of the momentum resolution could also be fulfilled, which leads to atomic momentum patterns less than 0.6 ℏkL
. To identify and remove systematic noises, we introduce the methods based on the principal component analysis (PCA) that reduce the noise in detection close to the

1
/

2

of the photon-shot noise and separate and identify or even eliminate noises. Furthermore, we give a proposal to measure precisely the local gravity acceleration within a few centimeters based on our study of ultracold atoms in precision measurements.
Multi-parameter global calculations of fission fragments using a simplified two-dimensional scission-point model *
Authors: Wei Kang , Zhang Hong-Fei , He Zhi-Xuan , Wang Xing-Yu , Guo Shu-Qin , Hu Bi-Tao
Published: December 2020

Exploiting the concept of the dinuclear system, the interaction potential energy of two fragments that are quite close to each other is analyzed. A semi-classical method is used to calculate fission fragment yields using a simplified two-dimensional scission-point model. By considering the tip-to-tip orientation at the scission point of the fission process, we investigate the mass, charge, and kinetic-energy distributions of the fission fragments, for excitation energies in the 0-20 MeV range. Our results show that the fission fragment distributions are reproduced quite well, including the recent experimental results for the isotone chain [D Ramos et al. Phys. Rev. C 97, 054612 (2018)]. Thus, the simplified model is useful for multi-parameter global measurements of fission products.
Strong Coupling Constants of the Doubly Heavy Spin-1/2 Baryons with Light Pseudoscalar Mesons
Authors: Rostami S. , Azizi K. , Olamaei A. R.
Published: December 2020

The strong coupling constants of hadronic multiplets are fundamental parameters which carry information about the strong interactions among participating particles. These parameters can help us construct the hadron-hadron strong potential and gain information about the structure of the involved hadrons. Motivated by the recent observation of the doubly charmed

state by LHCb, we determine the strong coupling constants among the doubly heavy spin-1/2 baryons,

,

and light pseudoscalar mesons,

, K,

and

within the framework of the light cone QCD sum rules. The obtained results may help experimental groups in analysis of the related data at hadron colliders.
STS36 XXXVI Siberian Thermophysical Seminar
Authors: Alekseenko S. V. , Markovich D. M. , Kuibin P. A.
Published: December 2020

The Siberian Thermophysical Seminar (STS) has been traditionally held at Kutateladze Institute of Thermophysics SB RAS in Novosibirsk Akademgorodok since 1960. This area being thirty kilometers away for the city represents a largest scientific center in the easter part of Russia with 35 multidisciplinary institutes spread around Akademgorodok.

List of Editorial Committee, Organizing Committee, Chairman, Deputy chairman, Scientific secretaries, Technical committee chairman, Members of the Organizing Committee and Scientific and advisory committees are available in this pdf.
The turbulent flow structure in a wall jet blown through cylindrical holes into a transverse trench. Experiment and numerical simulation
Authors: Chokhar I A , Ochered’ko A I , Pakhomov M A , Philippov M V , Terekhov V V
Published: December 2020

The results of experimental and numerical studies of the turbulent flow structure of a wall gas jet injected through round holes into a transverse trench are presented. It is shown that the main advantage of this method of coolant supply in comparison with the classical blowing through cylindrical holes in the protected surface is achieved at large blowing ratios. At that, the formation of vortex structures inside the trench ensures more uniform output of the secondary flow in the transverse direction. Comparative analysis with the data of our measurements indicates a quantitative correspondence between the results of the experiments and simulations.
The Flow Crisis and an Inner Source of Heating in the Vortex Tube
Authors: Pravdina M Kh , Kabardin I K , Polyakova V I , Gordienko M R , Yavorsky N I
Published: December 2020

The analysis of current complex experimental investigation of the vortex tube with square cross section is made focusing on the criticality of the inner flow in the framework of the flow crisis concept. The criticality condition is proved to take place in the vortex tube by operating with LDA obtained velocity experimental data. As the measured axial velocity exceeds the calculated velocity of centrifugal elastic waves on the boundary between the longitudinal circulation zone and the near wall swirling jet, two scenarios are supposed possible for the transition of the supercritical state to a subcritical one, similar to the vortex breakdown in a swirling jet at its discharge into the quiet liquid volume: the mild oscillations or a series of hydraulic jumps become possible, leading to a flow pattern choke change with the transformation to heat of excess kinetic energy.
Heat transfer behind a sudden expansion in a round tube with variation of the expansion ratio
Authors: Terekhov V I , Bogatko T V
Published: December 2020

The results of a numerical study of the influence of a step height on the flow structure and turbulent heat transfer in the zone of flow separation, attachment and relaxation are presented. The range of Reynolds numbers is ReD1 = 6.7·103-13.3·104. The degree of tube expansion varies within ER = (D2/D1)2 = 1.085 ÷ 4. In the work will show how exactly the ratio of tube expansion affects hydrodynamics and heat transfer in the separation area. When increasing ER the separation area lengthens and becomes more extensive: from 5 to 12 step heights (5h - 12h). Heat transfer is not so intensive, Numax decreases by the factor of 2.5. The coordinate of the maximum heat transfer Numax moves downstream. Comparison the calculation results with the experimental data of other authors is presented. A correlation formula allowing calculation of the separated flow with consideration of the degree of tube expansion is presented as generalization of data obtained.
Investigation of multistage air-steam-blown entrained-flow coal gasification
Authors: Nikitin A D , Abaimov N A , Butakov E B , Burdukov A P , Ryzhkov A F
Published: December 2020

The aim of the work is using an experimental-computational method to study the process of air-steam-blown entrained-flow gasification of coal with multistage air supply. To achieve this aim, the experiment was conducted on a plant consisting of a swirler into which coal and air are supplied, and a reaction chamber into which steam and multistage air are supplied; the experiment was numerically simulated using a validated CFD model; and the process under study was analysed using the obtained experimental and calculated data. The conducted experimental and computational studies of air-steam-blown gasification allowed determining the effect of steam supply and multistage air supply on the features of the gasification process. Steam injection lowers the temperature of the gas mixture and increases the concentration of hydrogen due to the hydrogasification reaction. The air supply to the reaction chamber increases the temperature of the mixture due to the burning of part of the syngas, while the syngas heating value is reduced by an appropriate amount. The maximum concentration of the syngas combustible components (and hence syngas heating value) is observed before the second point of air supply to the reaction chamber.
Nonlinear steady-state traveling waves in a rivulet flowing down an inclined tube
Authors: Aktershev S P , Alekseenko S V , Bobylev A V
Published: December 2020

The theoretical model based on long-wave approach is developed for the description of waves in rivulet flowing on the bottom surface of an inclined cylinder. The model equations are derived on the weighed residual method by projecting Navier-Stokes equations on the system of basic orthogonal polynomials. The simplest case of quasi-two-dimensional waves is studied in detail. The characteristics of nonlinear steady-state traveling waves in the rivulet are obtained for the first time. The results of calculations are in good agreement with experimental data for various liquids in a wide range of parameters.
The study of gas injection modes from a long tube to a channel filled with liquid
Authors: Alekseev M V , Lobanov P D , Svetonosov A I , Lezhnin S I , Pribaturin N A
Published: December 2020

The results of experimental and numerical studies of the gas phase injection into the liquid column and sudden gas-liquid interaction are presented. Experimental study was performed by means of high-speed shadowgraph and analysis of signals of pressure transducers. The numerical part of the work was carried out using the OpenFOAM software. The data about void fraction distribution and pressure evolution are presented. In general, a good agreement between the experimental and calculated data was found. The data obtained can be used for verification and validation of different numerical codes, as example ones for the prediction of the process of the steam generation leakage on nuclear power plant.
Experimental study of gas-liquid flow in a rectangular microchannel using LIF method
Authors: Bartkus G V , Kuznetsov V V
Published: December 2020

This paper aims at experimental study of gas-liquid flow in a horizontal rectangular hydrophilic microchannel with a cross-section of 200×400 μm. The ethanol and nitrogen are used as working liquids and gas accordingly in the microchannel with crossflow T-mixer at the channel inlet. Experimental data are obtained using high-speed visualization, laser flow scanning, and LIF method. The elongated bubble flow and transition flow are observed in the hydrophilic rectangular microchannel depending on gas and liquid flow rates. Using the LIF method, the non-uniform liquid film distribution is observed in the channel cross-section. The liquid film thickness is measured for elongated bubble flow and transition flow and compared with the Taylor law.
Simulation of conjugate heat and moisture transfer in multilayer porous materials with ventilated channels
Authors: Borodulin V Yu , Nizovtsev M I
Published: December 2020

A physical and mathematical model for calculating the thermal and moisture state of the facade of a building with ventilated channels has been developed. The model is based on the joint solution of a system of non-stationary differential equations of heat and moisture transfer in multilayer porous materials. In addition, equations describing heat and mass transfer in ventilated air channels are included in the model. The calculations of the thermal and moisture state of the brick wall of the building, insulated from the outside with heat-insulating panels with ventilated channels, have shown that the selected geometry of the ventilated channels provides a low level of moisture content in the facade materials.
The study of the hydrodynamics of bubble downflow at small gas-content by means of PIV / PFBI
Authors: Evdokimenko I A , Lobanov P D
Published: December 2020

Experiments on evaluation of the effect of bubbles on the hydrodynamic structure of two-phase bubbly downflow were carried out by means of PIV / PLIF method. Experiments were performed at Re = 5000 and gas flow rate ratio β = 1%. Data were obtained on the distribution of liquid velocity and its fluctuations, as well as on the mean bubble diameter. The results were processed using a computer bubble detection algorithm. To validate the received data, they were compared with the results obtained in [1] for the same pipe using electrochemical method. A good agreement was found for R. M. S. of liquid velocity distribution for different methods.
Influence of a soluble surfactant on the wave characteristics of a liquid film flow
Authors: Guzanov V V , Bobylev A V , Kvon A Z , Kharlamov S M
Published: December 2020

In this paper we present results of experimental investigation of the influence of soluble surfactant (Triton X-100) on wave characteristics of vertically falling liquid film in the range of film flow Reynolds number 25 < Re < 95. Shadowgraph technique is used to analyze wave patterns on the whole length of the test section (140 cm). Film thickness fields obtained with the help of high-speed Laser Induced Fluorescence (LIF) technique in two areas in the bottom part of test section allow analyzing statistical characteristics of the film flow. Expectedly, adding surfactant suppresses wave motion. For some surfactant concentrations the absence of waves is observed in the whole test section. For other concentrations the wave repetition rate decreases with distance from the liquid inlet. Analysis of spectral characteristics reveals that for water with some concentrations of surfactant, as for pure liquids, the steady-state three-dimensional wave regimes are observed. The characteristics in such flow regimes differ from the characteristics of pure water flow.
Experimental study of dynamic contact angles in liquid-liquid microfluidic plug flow with partial wetting
Authors: Kovalev A V , Yagodnitsyna A A , Bilsky A V
Published: December 2020

Partial wetting of walls by immiscible liquids in microfluidic flows is a crucial parameter for heat and mass transfer applications. Dynamic contact angles, which characterize wettability, are studied experimentally for different liquid-liquid sets in microchannels with 200×400 μm and 120×240 μm cross-sections. An appropriate algorithm is chosen for meniscus shape approximation. Cox-Voinov law is found to predict correctly advancing contact angles in liquid-liquid flow. The generalized version of Cox-Voinov law is proposed for the liquid sets with different physical properties. Based on experimental data, new dependences of receding contact angle on contact line velocity are provided for the systems with concave and convex rear meniscus of a plug.
Explosive vaporization of two- and three component liquid mixtures on microheater
Authors: Kozulin I A , Bartkus G V , Kuznetsov V V
Published: December 2020

The explosive vaporization of two-component mixtures of ethanol-water and three-component mixtures of acetone-ethanol-water during pulse thermal loads on the microheater during isobaric heating has been investigated. Microheater fabricated using MEMS technology presents the multilayer thin-film structure with the central Ta-Al layer heated by pulse electric current. The optical method based on measuring the laser intensity reflected from resistor surface recorded the characteristics of explosive vaporization. The dependence of the temperature of nucleation and the time of explosive vaporization on the rate of temperature growth and heat flux density are obtained.
Three-dimensional modeling of dynamics of liquid dielectric droplets on a wettable surface in the electric field
Authors: Kupershtokh A L
Published: December 2020

Three-dimensional non-stationary modeling of liquid dielectric droplets on a wettable surface in an electric field is performed. The distribution of the electric field is calculated by solving the equation for the electric field potential. The lattice Boltzmann method is employed to describe the hydrodynamic processes with gravitational, electrostatic, and capillary forces. A hemispherical droplet is placed on the surface of the lower electrode. Two variants of the droplet behaviour are observed. The droplet can acquire its equilibrium shape after several oscillations or elongate unlimitedly up to its destruction.
The numerical study of the flow regimes of two-phase oil and displacing agent mixtures in straight microchannels simulating a pore or crack in the rock formation
Authors: Lobasov A S , Minakov A V
Published: December 2020

The calculated study of the flow regimes of two-phase oil and water mixture in straight microchannels simulating a pore or crack in the rock formation was carried out. It was shown as a result of the literature survey that all modern, industrially developed methods of the oil recovery from the oil reservoirs is considered as unsatisfactory in all oil-producing countries. The average value of the final oil recovery is varied from 25% to 45%, so, it is easy to count, that residual or unrecoverable oil reserves in the subsoil reach an average of 55-75% of their initial values. Also, it was found, that the use of micro and nanotechnologies in a broad sense is one of the possible and promising ways to solve these problems. A numerical method called «Volume of Fluid» (VOF) was used to simulate the two-phase flows of oil and displacing agents in the considered microchannels. It was proposed to use the dimensionless number, called Regime number, to describe the different flow regimes of oil/water mixture and transitions between these regimes. The plug flow, the slug flow, the parallel flow and the emulsion flow regimes were observed.
Influence of stirring working area on the synthesis of freon 134a hydrate by the method of explosive boiling of liquid hydrate-forming gas in volume of water during decompression
Authors: Meleshkin A V
Published: December 2020

The presented work is part of a comprehensive experimental study aimed at finding the optimal operating parameters by the method of explosive boiling of liquefied hydrate-forming gas in a volume of water. The results obtained and published earlier showed the high efficiency and productivity of this method. This paper presents a study of the effect of the stirrer speed during the decompression of the working section on the gas hydrate synthesis.
Simulating waves on a horizontal liquid film entrained by a gas flow
Authors: Tsvelodub O. Yu. , Arkhipov D. G.
Published: December 2020

Nonlinear waves on a horizontal liquid film surface are considered. The effect of adjacent gas flow is taken into account through the data on shear stress at the film-gas interface obtained by the Boussinesq model of turbulence. A model nonlinear equation for the film thickness deviation from the undisturbed level is used to simulate nonlinear wave modes. Weakly nonlinear steady-state travelling solutions of this equation with wave numbers located in the vicinity of neutral wave numbers are constructed analytically. The evolution of periodic perturbations with wave numbers lying in the depth of the linear instability region is also considered numerically. Several typical scenarios of their evolution have been identified.
Bubble dynamics during flow boiling in a flat 0.6 mm high channel
Authors: Belosludtsev V V
Published: December 2020

The vapour bubble dynamics during subcooled flow boiling in a flat microchannel with the height of 0.6 mm was investigated using high-speed visualization. Nucleate flow boiling was maintained by localized heat source. The data on the bubble dynamics was compared with well-known classic growth correlation formulas. The obtained data have shown that the bubble size can reach the channel height in about 0.1 ms, which can lead to heat transfer crisis in channels with local heating.
Heat transfer in the falling liquid film on an array of horizontal tubes with MAO coating
Authors: Pavlenko A N , Pecherkin N I , Volodin O A , Kataev A I , Mironova I B
Published: December 2020

The paper presents investigation results on heat transfer of falling liquid films of Freon R21 on an array of horizontal tubes with porous Al2O3 coating obtained by the method of microarc oxidation (MAO coating). The microcharacteristics of samples (porosity, thickness, surface roughness) were measured. The results of measuring heat transfer coefficients on the surface of an aluminum tube with a MAO coating and a reference smooth tube were compared. Heat transfer on the surface of the tube with a porous coating was lower than on a smooth reference tube. It was shown that to intensify heat transfer on a surface with a MAO coating, it is necessary to increase the porosity of the coating and decrease its the thermal resistance.
Heat transfer at boiling on a vertical modified surface
Authors: Pavlenko A N , Zhukov V E , Slesareva E Yu
Published: December 2020

Modification of heat transfer surface through additive technologies (3D printing) is a very promising direction, since it allows organizing surface structures of any complexity with high reproducibility of parameters. This paper presents investigation results on heat transfer at boiling of freon R21 on a flat, vertically oriented brass surface modified with a copper coating using 3D printing. The heat-transfer surface is modified using 0.5 mm thick and 4 mm wide 3D-printed plates. The plates are made of copper spherical granules with an average diameter of 50 μm by laser welding of granules. The plates are fixed on the heat transfer surface by spot soldering. The experiments are carried out under conditions of large volume at a pressure of 0.18 - 0.21 MPa, which correspond to equilibrium temperatures of 25 - 30°C. The heat flux density varies in the range of 700 - 410000 W/m2. Experiments are carried out on the heat transfer surface before modification under the same conditions, but the surface is oriented horizontally. The experimental data show that for a modified heat transfer surface in the range of heat flux density from 1.8·104 to 3·105 W/m2, the heat transfer coefficient changes little and is approximately equal to 1·104 W/m2K. In the range of heat flux density less than 2·105 W/m2, the value of heat transfer coefficient on a modified heat transfer surface is up to 4 times greater than on a smooth horizontally oriented heat transfer surface without coating.