bluuebunny/crossref_metadata_2025 huggingface dataset:
Estudio de la manufactura y/o uso de instrumentos de trabajo y elementos de adorno de concha desde la metodología del análisis funcional
Authors: Cuenca Solana David , Clemente Conte Ignacio , Oliva Poveda Mónica , Gutiérrez Zugasti Igor
Published: April 2023

La traceología o análisis funcional se ha mostrado desde sus inicios como disciplina dentro de la Arqueología (Semenov, 1957) como una eficaz herramienta de acercamiento a la manufactura y uso de elementos materiales arqueológicos. Esta metodología se basa en el análisis macroscópico y microscópico de las huellas generadas en la superficie de los objetos durante su manufactura y/o uso, así como en la inferencia, a través de la experimentación analítica, respecto a como fueron realizados y/o utilizados. Las aplicaciones de esta metodología sobre materiales no líticos (hueso, asta, madera o concha) han sido bastante escasas, ya que generalmente estos objetos han sido analizados desde una perspectiva morfotipológica. Esto ha generado un menor desarrollo de una base metodológica específica para el estudio funcional de soportes con unas características físico-químicas y de conservación más heterogéneas en comparación a los elementos líticos. Sin embargo se trata de una metodología con gran potencial para extraer información acerca de la manufactura y uso de los objetos de concha, centrando el interés no en la morfología, si no en el proceso de manufactura y consumo de estos instrumentos de trabajo y/o adornos como vía de estudio de las sociedades del pasado.
La ocupación de la costa durante el Mesolítico en el Oriente de Asturias: primeros resultados de las excavaciones en la cueva de El Mazo (Andrín, Llanes)
Authors: Gutiérrez Zugasti Igor , González Morales Manuel R. , Cuenca Solana David , Fuertes Natividad , García Moreno Alejandro , Ortiz José E. , Rissetto John , De Torres Trinidad
Published: April 2023

La aparición de restos de Paracentrotus lividus en yacimientos arqueológicos supone una importante fuente de información que no siempre es posible valorar debido a la dificultad de cuantificar los restos y su aporte al conjunto estudiado. Recientemente, diversos autores han diseñado sistemas de cálculo para el NMI basados en el aparato bucal del erizo o sistemas de identificación interespecífica en base al aparato genital del mismo. En este artículo se presenta un sistema de cálculo de NMI basado en la aplicación de las Categorías de Fragmentación sobre el aparato genital. Este método se ejemplifica a través del estudio de los restos presentes en los yacimientos de Punta Atalaia y A Lanzada (Galicia, España). La combinación de éste sistema con los ya existentes, permite amplificar la identificación y contabilización de Paracentrotus lividus en yacimientos arqueológicos.
Moluscos dulceacuícolas en yacimientos arqueológicos: el registro en la provincia de León (Península Ibérica)
Authors: González Gómez de Agüero Eduardo , Bejega García Víctor , Fernández Rodríguez Carlos , Fuertes Prieto Natividad , Álvarez García Juan Carlos
Published: April 2023

En este artículo, se presentan los resultados del análisis de los restos de bivalvos de agua dulce recuperados en excavaciones arqueológicas de la provincia de León (España). El registro de estos moluscos es continuo al menos desde la Edad del Bronce hasta época medieval. Sin embargo, el limitado número de restos que suele estar presente y la ausencia de marcas vinculadas con la actividad antrópica, genera dudas sobre el significado cultural de su presencia.
A matter of taste? Mode and periodicity of marine mollusc exploitation on the Mediterranean island of Favignana (Ègadi Islands, Italy) during its isolation in the early Holocene
Authors: Mannino Marcello A. , Thomas Kenneth D. , Crema Enrico R. , Leng Melanie J.
Published: April 2023

La explotación de los moluscos marinos por parte de las sociedades cazadoras mediterráneas se incrementó a partir del Paleolítico Superior, si bien el papel desempeñado por este recurso raramente ha sido investigado en profundidad. Un marco ideal para abordar tal cuestión es el archipiélago de las Egadi, la mayoría de cuyas islas quedaron definidas como tal durante el Holoceno como resultado de la subida del nivel del mar. En este trabajo presentamos los resultados del análisis de las colecciones malacológicas recuperadas en las excavaciones de 1972 en Grotta d’Oriente, una cueva en la isla de Favignana ocupada entre el final del Pleistoceno y primera mitad del Holoceno. Los moluscos marinos, especialmente los caracoles marinos de litoral rocoso (Patella y Osilinus), fueron transportados para su consumo a lo largo de toda la ocupación, esporádicamente en el Mesolítico temprano pero de forma más intensa y a lo largo de todo el año durante el Mesolítico tardío y el Neolítico. El aislamiento progresivo de la zona generó una mayor intensidad de marisqueo aunque no una sobrexplotación a largo plazo de todos los gasterópodos de la línea de costa, a pesar de la vulnerabilidad de estos moluscos a la depredación por parte del hombre. Los datos arqueozoológicos e isotópicos sugieren que el marisco constituyó una útil fuente de proteínas para los ocupantes de la Grotta d’Oriente, si bien el papel principal de los moluscos marinos seguramente fue el de proveer nutrientes no siempre disponibles en las fuentes alimentarias de origen terrestre que constituyeron en todo momento el elemento principal de la dieta.
Acumulações de conchas mortas de moluscos na ilha da Ínsua (Caminha, Portugal)
Authors: S. Cabral João Paulo
Published: April 2023

De la información recogida por las crónicas históricas franciscanas de Fray Manuel da Esperança (1666) y Fray Pedro de Jesús María José (1760), encontramos en el Archivo del distrito de Braga una transcripción de un documento del siglo XVIII compuesto de dos partes (fechadas en 1441 y 1467) sobre las conchas de la isla de Insua. De acuerdo con la primera parte, la alcaldía de Caminha estuvo grabando impuestos a las conchas que los monjes franciscanos recogían en Insua. Los franciscanos protestaron y lograron detener los gravámenes. No obstante, años después la alcaldía volvió a imponer dicho impuesto, ya que en la segunda parte del documento, la casa de Vila Real, que poseía el Señor de Caminha desde 1464, informaba a la alcadía, ya que es él quien posee las rentas de Caminha. Tal conflicto en torno a este recurso natural remite a la importancia y abundancia de las conchas en esta isla. Dicha importancia derivaría de su uso en la confección de cal (lo cual menciona Manoel da Esperança), un ingrediente indispensable en la época en la preparación de mortero –necesario para la construcción– así como su uso en agricultura como fertilizante. Para confirmar la abundancia de conchas en Insua y comprender la dinámica de las acumulaciones, se realizó un trabajo de campo en el año 2010. Se constataron grandes acúmulos de conchas, especialmente en las zonas occidental y meridional de la isla, con masas que superaban las 10 toneladas. Los acúmulos estaban dominados por cuatro taxones (Mytilus galloprovincialis, Nucella lapillus, Patela spp. y Gibbula umbilicalis), con algunos ejemplares alcanzando tallas muy notables. Los moluscos fluviales y de estuario eran minoritarios. Se concluye que estos acúmulos derivan de ejemplares locales que las tempestades y la mortandad natural se ocupan de agrupar. La abundancia y riqueza del recurso se debe a la localización de la isla, donde las corrientes mezclan aguas ricas en nutrientes, en especial las que aporta el río Miño. En conjunto, estos concheros constituyen los más importantes de la costa continental portuguesa. Su uso es un caso raro (o único) de uso de conchas para la producción de cal en el Portugal medieval. Los resultados del estudio biológico validaron la autenticidad del documento analizado y de las crónicas franciscanas.
Factors Associated with Smartphone Dependence of Late School-Aged Children: A Focus on Grit and Family Strengths
Authors: Je Minji , Lee Ji-Won
Published: April 2023

This study was to identify the factors influencing smartphone dependence among late schoolaged children, focusing on grit and family strengths.A cross-sectional descriptive study was conducted with 218 children in grades 5 and 6 who were recruited from elementary schools in U and Y cities. The data were collected through self-reported questionnaires, including smartphone dependence, grit, family strengths and general characteristics, for the month of December 2019, just before the novel coronavirus pandemic after obtaining approval from IRB. The collected data were analyzed using multiple regression.Smartphone usage time, the main purpose of smartphone usage (game and social networking), and grit were identified as significant factors of smartphone dependence. This model explained 38% of the total variance showing the variable of grit with the greatest variance.A strategy to develop grit is needed to reduce smartphone dependence among late school-age children.
Effect of High Fat and Cholesterol Diet on Total Blood Cholesterol Levels in Pregnant Wistar Rats
Authors: Desmawati Desmawati , Mahdiyah Annisa Yuda , Kadri Husnil
Published: April 2023

Hypercholesterolemia during pregnancy is a physiological condition resulting from increased insulin resistance, lipoprotein synthesis, and lipolysis in adipose tissue, which mobilizes lipids as an energetic substrate for fetal growth. Consumption of foods high in fat and cholesterol may lead to an increase in total blood cholesterol levels during pregnancy due to saturated fat and cholesterol contents that will increases the synthesis of lipoproteins in the blood. The objectives of this study were to determine the effects of high fat and cholesterol diet on the total blood cholesterol levels in pregnant Wistar rats. This study was a true experimental research using a randomized post-test-only control group design  conducted from November 2020 to October 2021on fourteen female Wistar rats that were divided into control and intervention groups. Cow brain was provided as the high fat and cholesterol diet and after the rats gave birth, blood was drawn from the heart. The total blood serum cholesterol levels were assessed  using Micro Lab 300 with the CHOD-PAP method and the data were analyzed using an independent t-test. This study showed that the mean total blood cholesterol levels for the control and treatment groups were 80.43±18.512 mg/dL and  142.57±24.786 mg/dL, respectively, which reflected a significant differences in the mean total blood cholesterol level between the control and treatment groups (p-value <0.01). In conclusion, a high fat and cholesterol diet affects the total blood cholesterol level in pregnant Wistar rats.
Correlation Analysis of Lactic Acid Level as A Predictor of Severity of Patients with Acute Appendicitis
Authors: Rudiman Reno , Ruchimat Tommy , Rossy Cytra Givanni
Published: April 2023

Perforated appendicitis is a leading cause of morbidity and mortality in all appendicitis cases, both for adults and children. Delay in preoperative diagnosis is the main reason for perforation. In previous studies, it was revealed that diagnostic modalities such as radiological examination and the current scoring system have not been able to predict the onset of perforated appendicitis. Serological biomarkers of lactic acid are associated with intestinal obstruction and ischemia. The increase in the serological value of lactic acid in perforated appendicitis compared to acute one was shown to increase significantly by 0.25 mmol/L (p<0.05) according to a previous study. This study aimed to determine the correlation between lactic acid level and the severity of appendicitis in patients visiting Dr. Hasan Sadikin General Hospital. This was a cross-sectional prospective analytic observational study on adult patients diagnosed with appendicitis who were admitted to the emergency room of Dr. Hasan Sadikin General Hospital from January 1, 2021 to June 1, 2021. Data analysis was performed using bivariate analysis and correlation tests of difference. This study involved 54 subjects with a mean lactic acid level of 2,5093 mmol/L (0.9 mmol/L - 11.8 mmol/L). In the complicated appendicitis group, 20 subjects (37%) was found to experience an increase in lactic acid (OR 1.07; 95% CI: -0.03-0.22; p=0.14). The correlation analysis showed the direction of negative correlation. Thus, it is concluded that there is no significant correlation between lactic acid level and the severity of appendicitis in patients with appendicitis.
Malaria Infection and Socioeconomics in Malaria Endemic Areas of East Nusa Tenggara, Indonesia
Authors: Fauziah Nisa , Anindhita Edina , Ekawardhani Savira , Afifah Deviyanthi Nur , Hutagalung Jontari
Published: April 2023

More than 1.1 million people, or 20.90% of the population in East Nusa Tenggara (NTT), Indonesia, live below the poverty line, making NTT the third province with the highest number of poor people in Indonesia. The region of NTT, which is well known as one of the endemic areas for malaria in Indonesia, also has the highest number of adults with low nutritional status. This study aimed to assess the influence of socioeconomic factors on malaria-endemic areas in eastern Indonesia. A cross-sectional study was conducted in East Nusa Tenggara from January to March 2020. Bivariate and multivariate analyses were then performed on 317 population data of adults with low socioeconomic status. It was found that one of the socioeconomic factors, i.e., the age, is significantly associated with malaria (p-value = 0.031; OR = 1.684) with 40 being the age with the highest association. Thus, age is associated with malaria incidence in endemic areas.
Early Antibiotic Use and Neonatal Outcomes Among Preterm Infants Without Infections
Authors: Yu Weiyin , Zhang Lan , Li Shujuan , Yan Weili , Bai Ruimiao , Yang Zuming , Shi Jingyun , Yuan Jing , Yang Chuanzhong , Cai Wenhong , Wang Yang , Zhang Yi , Gu Xinyue , Cao Xincheng , Huang Yihuang , Hong Luyang , Zhou Qi , Yang Yi , Lee Shoo K. , Jiang Siyuan , Cao Yun ,   the Reduction of Infection in Neonatal Intensive Care Units Using the Evidence-based Practice for Improving Quality (REIN-EPIQ) Study Group
Published: April 2023

OBJECTIVES

To determine whether use, duration, and types of early antibiotics were associated with neonatal outcomes and late antibiotic use in preterm infants without infection-related diseases.

METHODS

This cohort study enrolled infants admitted to 25 tertiary NICUs in China within 24 hours of birth during 2015–2018. Death, discharge, or infection-related morbidities within 7 days of birth; major congenital anomalies; and error data on antibiotic use were excluded. The composite outcome was death or adverse morbidities. Late antibiotic use indicated antibiotics used after 7 days of age. Late antibiotic use rate was total antibiotic use days divided by the days of hospital stay after the first 7 days of life.

RESULTS

Among 21 540 infants, 18 302 (85.0%) received early antibiotics. Early antibiotics was related to increased bronchopulmonary dysplasia (BPD) (adjusted odds ratio [aOR], 1.28; 95% confidence interval [CI], 1.05-1.56), late antibiotic use (aOR, 4.64; 95% CI, 4.19-5.14), and late antibiotic use rate (adjusted mean difference, 130 days/1000 patient-days; 95% CI, 112-147). Each additional day of early antibiotics was associated with increased BPD (aOR, 1.07; 95% CI, 1.04-1.10) and late antibiotic use (aOR, 1.41; 95% CI, 1.39-1.43). Broad-spectrum antibiotics showed larger effect size on neonatal outcomes than narrow-spectrum antibiotics. The correlation between early antibiotics and outcomes was significant among noncritical infants but disappeared for critical infants.

CONCLUSIONS

Among infants without infection, early antibiotic use was associated with increased risk of BPD and late antibiotic use. Judicious early antibiotic use, especially avoiding prolonged duration and broad-spectrum antibiotics among noncritical infants, may improve neonatal outcomes and overall antibiotic use in NICUs.
Effects of wine processed Polygonatum polysaccharides on immunomodulatory effects and intestinal microecology in mice
Authors: Lu Tulin , Guo Zhi-jun , Li Xiaoman , Chen Peng , Li Yu , Zhang Jiu-ba , Mao Chun-qin , Ji Di , Su Lian-lin , Gao Bo , Lu Tu-lin
Published: April 2023

Polygonatum sibiricum is a traditional Chinese medicinal and food homologous substance, usually used after processing with yellow wine. However, its main active ingredient, polysaccharide, has been less studied after wine processing. This study aimed to investigate the effect of Polygonatum polysaccharides after wine processing on the function of immunosuppressed mice and its related mechanisms. The yellow wine processed Polygonatum (YWPP) polysaccharides were extracted by the water extraction alcohol precipitation method. BALB/c mice were used to establish the immunosuppressive animal model with cyclophosphamide (CTX). The immunomodulatory effect of the YWPP polysaccharides Interleukin 2, interferon γ, immunoglobulin A, Immunoglobulin M, T lymphocyte subsets, and other indexes were detected by enzyme-linked immunosorbent assay, flow cytometry, and other technologies. To study the mechanism of immunomodulation of polysaccharides, 16s rDNA sequencing and Gas Chromatography/Mass Spectrometry (GC/MS) were used to analyze the changes of intestinal microbiota composition, diversity, and the content of short-chain fatty acids (SCFAs). The Spearman method was used to analyze the correlation between gut microbiota and various immune indexes and SCFAs. The results showed that the YWPP polysaccharides could significantly restore the body weight of immunosuppressed mice, improve the spleen and thymus, and regulate peripheral blood cell values. The YWPP polysaccharides can also effectively promote Interleukin 2, interferon γ, immunoglobulin A, and immunoglobulin M in immunosuppressed mice and regulate the expression of immune-related indexes. The YWPP polysaccharides promoted the production of SCFAs, significantly regulated the relative abundance of norank_f__norank_o__RF39, Rikenellaceae_RC9_gut_group, norank_f__ UCG-010, and norank_f__norank_o__Clostridia_UCG-014; reversed CTX-induced metabolic abnormalities of mouse gut microbiota; and normalized them. Spearman correlation analysis showed that the relative abundance of gut microbiota was significantly correlated with various immune indices and SCFAs. In conclusion, the YWPP polysaccharides can improve the immune function of CTX-induced immunocompromised mice, promote cytokine upregulation and the relative abundance of immune-related beneficial bacteria in mice, and regulate the gut microbiota, thereby regulating host immunity. The results of this study will provide a theoretical basis for the practical application of the YWPP polysaccharides, health product development, and diversified product development.
Importance of thermal conductivity and stress level during a phase (hydride) transformation in magnesium
Authors: Aptukov V. N , Tsirulnik I. I. , Skryabina N. E , Fruchart D.
Published: April 2023

There are many different systems of an autonomous energy storage including accumulators and storage devices for renewable energy. Systems based on reversible metal hydrogenation have recently been introduced. The selection of metals is based on considerations of temperature and pressure conditions of the hydrogenation/dehydrogenation cycle, as well as the desired storage hydrogen capacity. Magnesium is one of the main challenging metals with respect to these main conditions since having a hydrogen capacity up to 7.6 w.%. For Mg forming MgH2, it was soon established that the size of particles plays a critical role since the kinetics (rate) of hydride formation accelerates when the size of the particles decreases. The present study shows that the overall diameter of the particles is the main characteristic controlling the kinetics of hydride formation because of distinct issues. A distribution of the size entails a strong dispersion transferring the heat of reaction, which characterizes Mg to MgH2 phase transition. Moreover, the formation of MgH2, is accompanied by a great increase of the unit-cell volume, developing noticeable internal stresses within the surface layers of the particles, thus turning to a systematic flaking and a systematic decrease of sizes of the powder particles. The results of the numerical modeling comply with the experimental data. This makes it possible to predict the best size of the initial Mg powder able to achieve fast kinetics during hydrogenation. Furthermore, the present analysis demonstrates the best hydrogenation kinetics, not only when using fine powders, but also when the deviation from the average particle size is minimized.
Simulation of impact failure of tubular samples made of composite material, depending on the loading rate
Authors: Fedorenko A. N , Fedulov B. N , Lomakin E. V
Published: April 2023

In this paper, a model that takes into account the dependence of strength properties on the damage rate is considered for modelling of the impact failure of composite materials. The constants of the material model are determined on the basis of experimental diagrams to compression and shear impact loading of unidirectional composite, which exhibit a nonlinear dependence on the strain rate. The proposed model is implemented to the Abaqus finite element modeling software for the case of a three-dimensional stress state. As an example of numerical modeling, we consider tubular composite specimens made of carbon fiber with an epoxy matrix and layers of different orientations, which are commonly used for determining of characteristics of impact energy absorption. Diagrams of impact loading of the considered tubular specimens are obtained. The influence of the chamfer (taper of the cross-section) on the edge of a tubular specimen on the impact loading diagram at the initial stage of the process, which serves as the initiator of crushing, is studied. The proposed approach allows us to estimate the magnitude of the peak of the amplitude associated with the crushing of the chamfer. In addition, at the initial stage of loading, maximum strain rates occur, which entails the hardening of the material, also expressed in the loading diagram as an increase in the amplitude. If the analysis neglects the effects associated with the strain hardening of the material and the geometry of the chamfer, the result may be expressed in an underestimation of the reaction, especially at the initial stage of the process. The absence of the described effects in the model of composite structures may lead to significantly incorrect results with complete failure with zero reaction. The developed approach is effective in the design and testing of damping elements made of composite material with properties that are sensitive to the loading rate.
Identification of gyroscopic forces in the oscillatory system of a Coriolis flowmeter
Authors: Romanov V. A , Beskachko V. P
Published: April 2023

The phase difference between the oscillations of the Coriolis flowmeter (CFM) arms is the main experimentally observed parameter during measurements of liquid flow rates in pipelines. Usually, steady-state oscillations and known dependences between the flow rate and the measured phase shift are assumed. However, these conditions are met with a sufficient accuracy only for homogeneous and single-phase flows. For inhomogeneous and multiphase flows, the correction of measurements is necessary. This correction in most cases is empirical. However, to improve the methodology of Coriolis flowmeter measurements, more detailed information about flow-tube interactions is needed. The experimental obtaining of such data is expensive and laborious. On the other hand, this data can be acquired during numerical experiments on the CFM virtual prototype. However, to effectively simulate liquid flows, it is necessary to separate the contribution of gyroscopic and dissipative forces to the experimentally observed signal (phase shift). This problem is complicated by the fact that gyroscopic forces are not uniformly distributed along the length of the tube, and the model for dissipative forces is not sufficiently developed yet. In this work, gyroscopic forces were separated by the 3D finite element modeling of steady-state oscillations of a tube with the ideal (inviscid) liquid. We discussed the usage of the simulation results in a simplified discrete model. It is shown that the magnitude of the phase shift recorded by the flowmeter depends both on the features of the distribution of gyroscopic forces and on the elastic coupling of the natural vibrations of the elastic tube caused by the fluid flow. The influence of the tube shape on the experimentally observed phase shift was investigated. For the tube shapes considered in the work, the difference in the phase shift for the displacements of the sections of the installation of the recording coils reaches nearly 5 times. The parameters of both gyroscopic and elastic coupling depend on the shape of the tube, and a change in the shape of the tube can increase the gyroscopic coupling and decrease the elastic one, and vice versa. The creation of a simplified discrete model of the flowmeter based on the results of the 3D finite element calculations is discussed. The quantitative estimates of the integral parameters of the oscillatory system of the CFM are carried out, allowing one to compare both the magnitude of the gyroscopic forces arising during the flow of the liquid and the degree of conformity of the tube shape to the special requirements for the oscillatory system of the CFM.
ABOUT THE YIELD PLATEAU UNDER SIGN-VARIABLE LOADING
Authors: Rychkov B. A , Goncharova I. V , Rezin P. M
Published: April 2023

During tension of samples of low-carbon steels and some other plastic materials, the sharp yield point and the yield plateau are fixed on the deformation diagram. In this case, Chernov-Luders bands appear on the surface of the sample in the local section, which then propagate along the tension axis. The physical nature of the sharp yield point is established: the drop in the load after reaching the (upper) yield limit occurs as a result of dislocations being an extraction out of the cloud of the embedded atoms and vacancies (Cottrell's cloud). At the occurrence of the sharp yield point , the plastic strain is limited to a small area. When the sample deformation increases, the plasticity zone (the yield plateau is marked on the diagram at this time) expands, and the stress-strain state in this zone becomes almost homogeneous, if we do not consider its boundary with the elastic region. At the end of the yield plateau, the entire sample experiences a uniform plastic deformation, excluding its ends (galtels). From this point on, the strain diagram shows the of material hardening; presumably, this hardening occurred from the very beginning, but was hidden under the yield plateau. This is evidenced by the resulting strain-induced anisotropy. After unloading the sample, when the plastic strain front (in the form of Chernov-Luders bands) has not yet passed through the entire sample, and the Bauschinger's effect is observed with the subsequent change in the stress sign. The fact that after the occurrence of the sharp yield point , the plastic strain is not localized in a certain volume, similar to what occurs during the neck formation, but spreads along the sample, serves as proof of the material hardening due to plastic deformation immediately after the load falls. Therefore, if the plastically deformable part of the sample did not have a hardening of the material due to the plastic strain growth, it would not be able to spread to the elastic part of the sample. This paper presents the experimental data of the sign-variable torsion of the thin-walled tubular samples of steel 45 in the annealed state. The deformation atdiagram of the occurrence and development of the yield plateau in distinct sections along the length of the test sample is obtained. The material hardening diagram hidden under the yield plateau is reconstructed using the well-known Masing's principle.
The Numerical simulation of composite sandwich cylindrical shells reinforced with circular frames under local loadings
Authors: Sukhomlinov L. G , Shivrin M. V
Published: April 2023

The paper considers a woven fabric (based on fiberglass) composite structure in the form of a foam core sandwich cylindrical shell reinforced with circular frames, under the action of local loads applied to the frames. A technique is described for obtaining a numerical solution (with the confirmed reliability) to the problem of the stress-strain state of this type of structure using two alternative computational models, one of which is based on the numerical integration method, and the other one is based on the finite element method. The first model is developed by adopting a scheme, in which the frames are considered as short cylindrical shells obeying the single normal hypothesis. The foam core sandwich sections connected to them are considered within the framework of the zig-zag theory of soft core sandwich shells based on the assumption of incompressibility of the core along thickness. In this case, the corresponding calculation problem is formulated in the form of systems of algebraic and differential (in partial derivatives) equations for each of the shell sections being considered, which are supplemented by kinematic and force conditions at their joints, as well as boundary conditions at the left and right ends of the structure. The problem solving for each harmonic number is reduced to solving a set of boundary value problems for systems of 8 and 12 linear ordinary differential equations of the first order, related by conditions at the specified joints and using the procedure for expanding the parameters of the stress-strain state and applied loads into Fourier series in the circumferential direction. The solution algorithm is constructed using the numerical integration procedure in the orthogonal sweep version combined with the displacement method procedure (to satisfy the conditions at the joints). The declared finite element model is built within the ABAQUS software package using S4 shell elements (for composite layers) and C3D20 volume elements (for frames and core). The formed model, when setting deliberately overestimated values of the corresponding elastic modules, can implement a situation close to fulfilling the set of hypotheses adopted when constructing the first model. Having fixed in such a situation the consistency of the calculation results on the basis of the alternative computational models constructed in this way and thereby confirming the reliability of the obtained numerical solution, we carry out the transition to the calculation using the real values of the mentioned modules and the analysis of their influence on the stress-strain state of the investigated sandwich shell. The presented example of the calculation of a composite sandwich cylindrical structure, one of the frames of which is under the action of two local axial loads, demonstrates the possibilities of the adopted modeling method.
DETERMINATION OF THE STRESS STATE AND THE FORCE OF DEFORMATION OF BALL-SHAPED BILLETS IN A CLOSED MATRIX
Authors: Ashkeyev Z. A , Andreyachshenko V. A , Abishkenov M. Zh , Bukanov Z. U
Published: April 2023

At the present stage of development of science and technology, the problem of improving the quality of metal products by integrating methods of severe plastic deformation into existing technological processes is urgent. Intense plastic deformation makes it possible to obtain nanostructured metallic materials with improved quality and an attractive set of properties due to the saturation of the metal with nanoscale defects. Spherical billets with two ends along the edges are a common form of metal products. For the manufacture of such metal products, the effect of mutual influence of all-round compression and ECAP pressing in a device for the implementation of equal-channel angular pressing in a closed matrix was used. The purpose of this study is to develop a theoretical approach to determining the stress state and deformation force of spherical blanks in a closed matrix. To achieve this goal, an integrated approach was used to determine the stress state and deformation force by the method of slip lines and computer simulation in the Deform-3D software package. Analysis of the results of the stress state of the workpieces obtained by the slip line method showed that a uniform stress state is formed with a predominance of the maximum compressive stresses. The combination of the latter with angular metal extrusion into the lateral channels of the matrix predicts the production of workpieces with sub-ultrafine-grained and/or nanostructure. By the method of joint solution of differential equations of equilibrium and plasticity conditions, as well as computer modeling, the deforming force of the blanks at the final stage of deformation, when the metal flows out into the lateral channels of the matrix, is determined. The analysis of the obtained results shows that the value of the deformation force obtained by the two methods is comparable with a difference of up to 2 %, which confirms the correctness of the obtained values.
Modeling of rubber-cord layers under quasi-static loading
Authors: Sheshenin S. V , Yikun Du , Chistyakov P. V , Artamonova N. B
Published: April 2023

Modeling a pneumatic tire with a strong change in shape causes the problem of choosing an adequate model for rubber-cord plies. Generally, the classical method of asymptotic homogenization is not suitable due to physical and geometrical nonlinearity for the strain up to 15 %. The known models used for simulation the entire tire as well as rubber-cord plies are analyzed. A choice is made in favor of modeling the plies using the stress anisotropic potential, which is an anisotropic function of the strain tensor invariants. The relationship of such a constitutive law with a quasi-linear constitutive equation in terms of stress and strain differentials is indicated. A convenience of these two types of constitutive equations in terms of numerical implementation is also given. A modification of the effective properties definition for an inhomogeneous layer is explained. The difference from the standard effective moduli definition is clarified. The arrangement of the cords is supposed to be approximately periodic and all cords to be equivalent to the effective fiber. Two models of a rubber-cord plies are described under such assumption. These are a model of an orthotropic material and a model of a transversely isotropic material. Computational experiments, which make it possible to determine the material parameters of anisotropic potentials, are pointed out. Real tests with a sample of rubber ply under slow quasi-static loading were conducted. Significant hysteresis was detected. It is shown that an additive model combining a hyper elastic material with Maxwell viscoelastic model provides good accuracy in stress dependence on the strain rate. The numerical procedure developed to calculate solution to the quasi-static problem of tire deformation is described. It is implemented in home-made computer code. A numerical example on the tire simulation is given. That is so-called breaking test, in which strong deformation is achieved and the developed model is applied to.
Analysis of multiaxial fatigue models based on the results of biaxial tests for aluminum alloys
Authors: Gabe A. A , Wildeman V. E , Yankin A. S
Published: April 2023

During operation, modern structures and their parts are subjected to complex cyclic loads. In this case, a complex stress-strain state can arise in products, which can lead to a significant decrease in their fatigue life. In this regard, the development of methods for predicting fatigue fracture of critical structures becomes urgent. The purpose of this work is to test a simple approach for describing multiaxial fatigue datasets presented in the literature and compare it with known multiaxial fatigue models. Within the framework of the study, actual experimental data was considered, containing experimental data on the multiaxial fatigue of aluminum alloys 2024-T3 and 2024-T4. The alloys are actively used in the designs of aircraft, ships and spacecraft. As a result, the Sines model and its modernized version were considered (taking into account the first invariant of the stress tensor with respect to amplitude values). At the same time, an approach was developed to determine the constants of the models based on the results of two variants of training experiments. The paper presents the results in the form of relationships of the predicted and experimental fatigue life, obtained using the Sines model and its modification for two types of training tests. In the final part of the work, a comparative analysis of the Sines model and its modification, Smith-Watson-Topper, Fatemi-Socie and its modification is carried out. The analysis showed that the modified Sines model significantly improves the predictive ability, the proposed model better described the experimental data than the traditional Sines model and the Smith-Watson-Topper approach. At the same time, the descriptive ability of the model is comparable to the Fatemi-Socie one.
Calculation of the thermal conductivity coefficient of nanocrystals
Authors: Severyukhin A. V , Severyukhina O. Yu , Vakhrushev A. V
Published: April 2023

Mathematical modeling methods are powerful tools in the design of various types of nanosystems and the analysis of processes taking place in them. Note that the main tasks of mathematical modeling in nanoscale systems are: the formation of nanoelements, the interaction of individual elements of the nanosystem, the determination of the structure of the isolated nanosystem in dynamic states, the calculation of the parameters of the nanosystem during its interaction with the environment, the calculation of the macro parameters of the nanosystem. With this work, we continue the consistent presentation of theoretical foundations, methods of modeling, and results of calculations of macro characteristics of nanosystems, based on the work on modeling of processes of formation and structure of different nanosystems. This paper provides the physical basis as well as numerical methods for calculating the thermal conductivity of homogeneous nanosystems. Computer simulation of the calculation of the thermal conductivity coefficient of silicon-based nanocrystals by molecular dynamics was carried out in the LAMMPS software complex. Equations describing multi-particle MEAM potentials are considered. The problem of determining the thermal conductivity coefficient has been solved in several steps. In molecular dynamic calculations, the value of the thermal conductivity coefficient can be calculated in various ways. This work uses the Green - Kubo formalism, which associates the autocorrelation function of heat flow with the coefficient of thermal conductivity. Temperature dependencies of thermal conductivity coefficient for silicon-based materials are determined. Calculations of thermophysical characteristics of homogeneous silicon-based nanosystems were made. The curves of the temperature dependence of thermal conductivity coefficient for systems of different dimensions are presented. Data obtained using MEAM potentials were compared with experimental data. It was found that the nature of the curves and the values obtained during the simulation are well consistent with the experimental data.
Two-dimensional model of grain boundary diffusion and oxidation
Authors: Chepak-Gizbrekht M. V , Knyazeva A. G
Published: April 2023

The grinding of the structure of materials is accompanied by a change in the physical and mechanical properties. This occurs largely due to the accumulation of energy and defects in the structure, which activates the diffusion of impurities contained in the material. The increase in the number of grain boundaries and joints can cause the inelastic behavior of the material, its additional chemical activation. For some metals and alloys this leads to strengthening, while for others it leads to rapid degradation of mechanical properties. Grain boundary diffusion in such materials is the main mechanism of transport of alloying components or harmful impurities, so its study is important. This paper presents a two-dimensional model of grain boundary diffusion in a material with an explicit structure assignment. The model takes into account the presence of chemical transformations that can determine the corrosion mechanisms under operating conditions. For simplicity of calculation the material structure is taken symmetrical and contains two phases: grains and a boundary phase. Diffusion and kinetic parameters of the phases may differ. The model is represented in dimensionless form so that the distances between neighboring grains or the widths of the boundary phase are the same and the grain sizes can vary. Depending on the ratio of phase sizes we can speak about micro- and nanocrystalline structure. The problem was solved numerically using implicit difference scheme and coordinate splitting. Diffusion and kinetic parameters, which are close to the parameters of oxygen grain boundary diffusion in titanium and titanium oxidation, respectively, were taken for the calculations. Integral concentrations reflect the dynamics (kinetics) of oxygen and oxides accumulation over the calculation area. Results showing the role of changes in the oxidation kinetics due to changes in the reaction constants in the phases and the phase size ratio are presented. The model can be useful for assessing the degree of influence of grain boundary diffusion on the oxidation process and the accompanying change in properties, as well as for setting up appropriate experiments.
The Simulation of the Nonlinear Consolidation of Porous Media
Authors: Sheshenin S. V , Artamonova N. B
Published: April 2023

In this paper, the general formulation of the problem of coupled deformation of a porous deformable medium with a fluid flowing through the pores is formulated, mathematically investigated and numerically implemented within the framework of physical and geometric nonlinearity. We present the formulation of the problem in velocities of solid phase displacements and the rate of pore pressure change in differential and variational forms. A phenomenological approach was used to formulate the mechanical model. The equations of the coupled consolidation model were derived from the general conservation laws of continuum mechanics using spatial averaging over a representative volume element. The consolidation model took into account the change in the porosity and permeability of the medium during deformation. The equations of filtration and porosity change, originally presented in Euler approach, were reformulated in Lagrangian coordinates of the solid phase using the relative fluid velocity according to ALE (Arbitrary Lagrangian - Eulerian) approach. The Gâteaux differentiation technique was used to linearize the variational equilibrium equations. For spatial discretization of the saddle system of equations, the finite element method (FEM) was used: quadratic serendipity elements for approximating the equilibrium equations and Brick type elements for approximating the filtration equation. To solve the system of equilibrium and filtration equations, a generalization of the implicit scheme with internal iterations at each time step by the Uzawa method was used. The results of numerical simulation of elastoplastic deformation of a water-saturated soil under load with fluid outflow are presented. To simulate the constitutive relations of elastoplastic deformation of soil under short-term loads, a generalization of S.S. Grigoryan's model to large deformations is proposed. The calculations were carried out in our own program code. The developed consolidation model can be used to simulate the formation of tracking ruts and unevenness of natural roads, as well as to calculate the uneven settlement of engineering structures.
Modelling the effect of vibrations on the surface tension of a liquid droplet using meshless methods
Authors: Davlyatshin R. P , Perminov A. V , Bayandin Y. V , Saucedo-Zendejo F. R , Trushnikov D. N
Published: April 2023

Application of vibration impacts for purposeful influence on such processes as drop formation, melt bath formation and crystallization of welding bead allows to control heat and mass transfer in liquid, crystallization process and shape of bead in technological processes of welding. Impact of vibration influences on nature of motion of liquid in the drop, which is reflected in the change of value of surface tension coefficient, is considered in the article. The mathematical model of the liquid flow considering surface tension force in formalism of smoothed particles hydrodynamics method is offered. This method allows direct consideration of the vibration effect by introducing additional boundary conditions. Verification of developed mathematical model is conducted in comparison with in-situ experiments, in which dependence of surface tension coefficient value on amplitude of speed of vibration influences was determined. To determine surface tension coefficient two methods were implemented: pending drop method and stalagmometric method. The implemented model satisfactorily describes the effect of decreasing surface tension coefficient for water. A series of numerical experiments for determining the effect of vibration influences on the value of surface tension coefficient for 12X18H10T steel grade was carried out. It was found that at vibration with speed amplitude equal to 2.0 m/s the decrease of surface tension coefficient value by 30 % is observed. Decrease in surface tension coefficient should facilitate the realization of continuous flowing of metal from the wire, which may positively influence the formation of metal during wire surfacing. Thus, the proposed mathematical model can clearly simulate the effect of vibration effects on the value of the surface tension coefficient and will allow the effect of vibration effects in additive manufacturing to be investigated in the future.
Low-cycle fatigue of V-notched cylindrical samples of bronze alloy
Authors: Abashev D. R
Published: April 2023

The article presents the results of experiments on cyclic loading of samples with an annular V-shaped notch and their mathematical modeling. The tests were carried out on specimens of the BrKh08-Sh alloy with a cyclic change in the tensile load from 0 to a given value. Under such loading, the material in the groove area is subjected to cyclic elastoplastic deformation, which leads to failure due to low-cycle fatigue. When testing samples using the digital image correlation method, the deformation of the material on the surface of the undercut was measured, which made it possible to determine the nature of the change in its range from cycle to cycle. Mathematical modeling of experiments is carried out according to the finite element method. For this purpose, models of elastic-plastic deformation and accumulation of material damages are introduced into the SIMULIA Abaqus software package. The plasticity model is based on the theory of flow under combined hardening. The damage accumulation model is based on the energy strength criterion. The article presents the basic equations used to calculate the models. The material parameters are determined and verified based on the results of a basic experiment on cyclic tension-compression of a smooth cylindrical sample under asymmetric rigid loading. Based on the results of the calculation, cartograms of stresses, deformations, and accumulated damages were constructed. It is shown that when the sample is unloaded, in the area of stress concentration close to the annular groove, compressive stresses arise, the values of which are close to the values of tensile stresses at the moment of application of the maximum load. The results of mathematical modeling are compared with the experiment. A comparison of the results was carried out in terms of the range of axial deformation of the material on the surface of the undercut and the number of cycles before failure.