bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of magnesium calcium alloys improved by rare earths addition for medical implants
Authors: Savin A , Novy F , Craus ML , Iftimie N , Steigmann R , Istrate B , Munteanu C
Published: September 2020

Biodegradable materials are used as alternative implants for orthopedic applications due suitable strength, fatigue resistance, ductility and biocorrosion resistance which are features for biodegradable implants. Mechanical properties can be improved by adding alloying elements. The decrease of the corrosion rate of Mg can be induced by modifying the structure and phase distribution. Thus, Mg alloys have been designed to meet the requirements of bone repair implant materials by adding = Calcium and Yttrium or Gadolinium. Mg based alloy with Ca and Y/Gd had been proved to be a biocompatible material, osteoconductive and biodegradable and can be used in bone repairs. The system is defined as Mg100-(n+x) Ca(n) RE(x), varying the RE concentration in order to slow the degradation process. Beside morphological combining characterization SEM, EDX, with non-invasive testing is required to be carried out the determination of mechanical characteristics. The interest in this study is to analyze the influence of RE over elastic properties of these alloys in order to choose the best values appropriate with human bones, using Resonant Ultrasound Spectroscopy and ultrasound method.
Monitoring techniques for carbon fibers reinforced plastics used as complex structures
Authors: Savin A , Sturm R , Bergant Z , Stanciu M D , Steigmann R , Dobrescu G S
Published: September 2020

Carbon fiber reinforced plastics (CFRP) have become an indispensable part of modern life. CFRP materials continue to be used in a large number of applications ranging from aerospace systems to automotive, industrial and consumer products. CFRP have evolved both in reinforcement and matrix. The epoxy resin was the most usually matrix for CFRP. The reliability of these materials is essential, especially when it comes to safety-relevant components. The service life of CFRP components is affected by aging processes or improper use. Nondestructive evaluation methods which can be applied for examination carbon/epoxy laminates, manufactured by autoclave processing method with different ply stacking sequences [0]8 and [(45/0)2]s are presented. The samples were realized from 4 plates of carbon-epoxy manufactured at the Faculty of Mechanical Engineering, University of Ljubljana, Slovenia. The paper present influence of thermal treatment and stacking sequence on damage delamination’s due to impact about mechanical properties. Ultrasound and electromagnetic nondestructive evaluation methods are used for good localization of damage and characterization composite materials and other techniques can provide complementary information once the damage location is known.
Practical method of obtaining different levels of seismic energy dissipation using viscous fluid protective system on bridges
Authors: Scheaua F
Published: September 2020

In order to achieve an optimal stability performance during transient vibratory actions the damping method is used for the bridge structures. Conventional approach would dictate that a structure must inherently attenuate or dissipate the effects of transient inputs through a combination of strength, flexibility and deformity. The damping level is being at low values at a conventional elastic structure and hence the amount of dissipated energy during transient vibratory actions is also in very low value. In the event of an earthquake, conventional structures usually perform high deformations which when situated beyond their elastic limits can cause the collapse. In such cases most of the dissipated energy amount is absorbed by the structure through localized damage as it fails. The concept of supplemental dampers added to a structure assumes that most of the energy amount input to the structure from a transient vibratory action will be absorbed, not by the structure itself, but rather by supplemental damping elements. Properly implemented, an energy dissipation system can be able to simultaneously reduce both stress and deflection within the structure elements. The fluid viscous protective system concept is presented as an optimum energy dissipation solution for bridge structure types. The operation of these devices is on the hydro-static principle of fluid flow through orifices of a special diameter value. In this paper it is presented an innovative functional and constructive model of fluid viscous device based on a practical design method which allows the controlled operation regime regarding the viscous fluid flow inside the device cylinder being able to provide considerable resistant force levels to relative motions between a bridge structural frames where is mounted and achieving considerable amounts of seismic energy dissipation when an earthquake occurs. For the constructive method of fluid viscous system model is adopted a practical constructive method aiming the direct control on the circulated fluid flow rate so that the device response force should be considerably larger, acting for limiting the relative movement of the structural frames and without introducing additional stiffness to the structural system to which it is attached, due to the elasticity of the working fluid type used. It represents an innovative method because of the special design orifices for fluid flow rate control used which, depending on the specific diameter values, can provide device different response force values and implicitly different dissipated energy amount levels based on the characteristic represented by the resistant force variation law according to the piston stroke.
The two-dimensional fretting contact with a bulk stress. Part II – Loading history and dissimilar elastic materials
Authors: Spinu S
Published: September 2020

The contact model for similarly elastic materials advanced in the companion paper is enhanced to account for the more general case of contacting bodies with different elastic properties. The latter contact model, involving dissimilarly elastic bodies under partial slip, is particularly difficult to solve due to the mutual interaction between the normal and the shear tractions. As opposed to the contact of similar elastic materials, pressure is affected by the shear tractions and vice versa. Therefore, the contact submodels in the normal and in the tangential direction are not independent. The connection can only be overcome in an iterative manner, by adding a new external loop to the contact algorithm, in which the solutions of the systems in the normal and in the tangential directions are mutually adjusted by successively solving both systems until convergence is reached. Moreover, with friction being a dissipative process, any state depends upon the process path, i.e., on all previous states attained during the loading history. The contact model is solved as a series of quasi-static states that are expected to replicate the loading path. Two levels of iterations are added to the model of similarly elastic materials, described in the companion paper, to account for the dissimilarity in the elastic properties. The contact process is reproduced on a prolonged loading history, consisting in the first fretting loops. The distributions of contact tractions are obtained using a technique for the fast computation of convolutions involving the fast Fourier transform. The conducted simulations prove the method robustness and its application in the modelling of the fretting processes.
Researches and constructive solution to enhancing the stiffness of the gantry type milling machines
Authors: Stan G , Zichil V
Published: September 2020

For machining of large size work pieces, CNC milling machines with moving bridge (known as Gantry Type milling machines) that have a large distance between the bridge columns, i.e. 4 to 7 meters are frequently required. This leads to a difficult guiding, driving and stiffening of the moving bridge. At the same time, the moving bridge is required during the cutting process by a number of forces, some of them fixed, others variable. The manufacturers of such machine tools sort out this problem by a “suitable” sizing of the moving bridge that involves large overall dimensions of the bridge, with major implications on its guiding. This work presents an innovative solution concerning the increase of the stiffness of the Gantry type bridge, so that the geometrical accuracy of the machine is preserved regardless the force variations in the guiding system of the moving bridge. This work sets out an interdependent connection between the variation of the requiring forces generated at a high extent by the location of the moving elements on the cross rail and the compensating forces in the guiding of the two columns of the bridge.
Contact stress simulation problem in case of thermal spray coatings
Authors: Stescu C , Chicet D , Tufescu A , Istrate B , Munteanu C , Strugaru-Iacob S
Published: September 2020

In this study was addressed the problem of the contact stress simulation, generated in the case of the loads applied on thermal spray coatings, by finite element modelling. Starting from the characteristic lamellar morphology of this type of coatings, consisting of splats, voids, oxidized or unmelted particles, the studied layers were assimilated to an anisotropic material. Thus, it was tried to establish the parameters necessary for modelling, so that they define as accurately as possible the studied material. The purpose of this study was to identify the maximum value of the tension developed in the point contact, on the depth of the analysed layer. This value was subsequently used to determine the limit values for in practice use of the coatings.
Improvement of machine tool accuracy through ball screw location optimisation in relation to the guideways of the axes
Authors: Stoica A , Stan G
Published: September 2020

An important role in obtaining a high positioning accuracy is also played by the location of the ball screw in relation to the guideways of each axis. This makes that noncompliance with the Abbé principle to lead to higher positioning deviations. The compliance with the Abbé principle is difficult to be achieved from the constructive point of view because the cutting forces differ in terms of direction, sense and value within the working space of the machine tool. This work develops a mathematical model that allows finding the location direction of the ball screw in relation to the guideways, so that the positioning accuracy is increased. The conditions that may influence the improvement of the positioning accuracy by increasing the guideway stiffness and settling the dimensions of the moving element are studied in this work, as well. The mode of locating the position encoder in case of direct measurement that, together with the noncompliance of the Abbé principle leads to affecting the positioning accuracy is also presented. The results have been obtained experimentally on a milling machine where the ball screws have been located symmetrically in relation to the main guideway.
Influence of cutting parameters on surface hardness in milling of AL6061T6
Authors: Tampu C , Chirita B , Cristea I , Zichil V , Schnakovszky C , Herghelegiu E , Carausu C
Published: September 2020

Milling is an important industrial common machining operation used to produce complex surfaces. Surface quality in milling operation is influenced by various factors such as cutting speed, cutting feed, depth of cut and chemical composition of the material. Surface quality is defined by roughness, residual stress and microhardness and is important in determining corrosion resistance and in fatigue crack initiation. The aim of the present paper is to analyse the influence of above-mentioned cutting parameters (cutting feed, cutting speed, depth of cut) on surface microhardness. Tests were conducted using a Coro mill 490 with a single insert that was indexed for every experiment, thus eliminating the influence of tool wear. Al 6061-T6, a material widely utilised in aircraft, defence, automobiles, and marine areas due to its good proprieties (good strength and lightweight) was used. Microhardness was measured on workpiece surface but also in the cross section of the workpiece, up to a depth of 1mm, in order to observe material state in subsurface layer. It was observed from the results that an increase of cutting speed have led to an increase of microhardness while a higher value for depth of cut has led to a lower value of microhardness. Feed rate has generated similar results with the depth of cut.
The process of optimizing the radial sliding bearing
Authors: Turof M
Published: September 2020

The problem of optimizing the bearing choice process, caused by the failures due to the short life of the bearings, caused by the difficult working conditions, is becoming more and more frequent.

By further optimizing the type of bearings used, we aim to both improve efficiency and productivity and reduce costs.

For the choice of a radial sliding bearing, the three basic steps are followed: calculation of the diameter of the shaft, verification of the bearing pressure, thermal calculation. If at least one of the last two is not appropriate, the designer must change the material, the cooling conditions or the length / diameter ratio and then recalculate the bearing.

The methodology of optimizing the choice of bearings involves the establishment of a set of initial constraints to reduce arbitrary recalculations.

In optimal design, we eliminate the drawbacks presented in usual design and we impose at the beginning some restriction for shaft material, deflection, cooling capacity, we determine the type of fit and tolerances, that is neglected in usual design.
Characterization of drying behavior and modeling of industrial drying process
Authors: Vasić M , Radojević Z
Published: September 2020

The general method for industrial chamber dryer optimization was reported in this paper. The first step in finding the most suitable drying regime is to characterized the clay raw material, especially its water loss at 2000C and to determine the critical drying rate inside the specially constructed laboratory dryer. These data provides us information if the product or the dryer is the bottleneck for the optimisation. If the optimization is justified geometry of the dryer, air mass flows, temperature, and humidity profiles inside the dryer as well as initial water content in the drying material, initial temperature of the products and the load of the dryer are required. Some of the previously mentioned data are only used to check if the chamber dryer is working properly, while the others are used as the initial parameters necessary for software simulation. In this paper two models for calculating the optimal drying parameters were used. The first model was developed from the comprehensive theory of the moisture migration during isothermal drying. The calculation software for setting up the non - isothermal drying regimes was reported in our previous papers. It is important to say that this model was not able to adequately predict the temperature raise within the drying products. In order to simulate the raise of the temperature of the roofing tiles during drying the second model was used. This simple receding drying front model was firstly reported by Kitcher. If both models are used simultaneously it is possible to calculate air temperatures, product temperature, absolute and relative humidity of the drying air, moisture content of the product, drying rate etc… It is important to mention that this approach can lead to the recommendations for changes inside the dryer before an optimized situation is achieved. One example of such situations is described in this paper in details.
Natural zeolites: prospects for heavy metal polluted soil remediation
Authors: Bocharnikova E A , Shabayev V.P. , Ostroumov V.E. , Demin D.V.
Published: September 2020

The environmental concerns related to oil extraction, transportation and refining include the pollution with heavy metals (HMs). Currently, there is a growing interest in the study of an influence of silicon-rich materials, including such natural minerals as diatomite, zeolite, and others, on the HM behavior in the environment with regard to their exploitation in soil remediation strategy. In greenhouse pot experiment, the effects of natural zeolite on the biomass of barley plants grown in artificially cadmium (Cd)-contaminated soil and Cd uptake and translocation were studied. Zeolite applied to soil at a low rate (0.15%) mitigated the Cd phytotoxicity and provided the same plant biomass production as in uncontaminated soil without zeolite. Zeolite stimulated development of root system. The application of zeolite at a low rate enhanced the phytoextraction process–cleaning up the soil from HM at the early (booting) stage of plant development.
The formation of nanoparticles in the process of ultrasonication of the pure water
Authors: Ivanova D D , Gorbachevskii M V , Novikov A A , Kuryakov V N
Published: September 2020

Ultrasonication is a very convenient method for the preparation of various dispersions. However, it is often not clear what influence the ultrasonication procedure is on the purity of the prepared dispersion. In this paper, we show that the prolonged ultrasonication of the pure water results in dispersion formation. We characterized the nanoparticles in the resulted dispersion by the TEM, DLS, conductivity, and zeta potential measurements. This work points to the possible source of contamination of the sonicated dispersions.
Monitoring of mechanisms of formation of corrosive aggressiveness of soils and grounds of underground gas pipeline routes and on its basis assessment of service life of gas pipes in various soil-climatic zones
Authors: Khudyakov O I , Reshotkin O V , Demin D V , Velikotskiy M A
Published: September 2020

The experience of studying the problem of corrosive aggressiveness of soils and grounds in terms of improving the reliability of Gazprom’s pipeline systems operation is summarized and presented. Soil factors causing surface corrosion of gas pipelines in soil conditions are studied. Based on the obtained results, it was suggested to evaluate not only the corrosive aggressiveness of soils and the gas pipe lifetime, but also the corrosive resistance of pipe metal in corrosive environments. Special attention is paid to the stress corrosion cracking formation mechanism.
Study on rheological properties of clayless drilling fluids influenced by fractional composition of carbonate weighting agents
Authors: Leushevaand V A Morenov E L
Published: September 2020

Study of the influence of weighting-bridging agents on technological parameters of drilling fluids is an important aspect in the development of washing fluid compositions, especially when drilling-in productive formations. At selection of weighting agents, it is often assumed that these substances are inert and do not affect the structural and rheological parameters of the fluid, but only increase the density (due to higher specific gravity) and lower the filtration parameters (due to an increase in the solid phase content). Paper presents experimental study to assess the effect of the fractional composition of carbonate weighting agents on structural and rheological parameters of a biopolymer drilling fluid used to drill-in a reservoir. Carbonate substances with an average particle size of 5 to 150 microns were used as weighting-bridging agents. Based on the data obtained, dependences of the main structural and rheological parameters of the drilling fluid on the size of the weighting-bridging agent’s fraction are revealed.
Method of signal identification based on wavelet analysis.
Authors: Loginov V A , Elnikov A V
Published: September 2020

The article presents the results of the development of a method for identifying the source of vibroacoustic impact on the sensitive element of the fiberoptic perimeter protection system of industrial facilities. The methodology was tested on the identification of signals from the following sources of vibroacoustic impact: impact over a certain period of time, or shaking the fence (t-impact); short-term impact type impact (ẟ-exposure). In the course of the work, polygon tests of the perimeter security system were conducted, a library of signals was compiled, and characteristic features of signals of various types of impact on the sensitive element of the system were identified. The main signal processing tools are the Fourier and wavelet transforms.
Biodegradation of polymer compositions with pro-oxidants
Authors: Lukanina Yu K , Popov A A , Khvatov A V
Published: September 2020

Oxo-biodegradable plastics are widely used as an alternative to well-known polyethylene and polypropylene. thanks to the polyolefin base, they have the necessary set of operating characteristics and are able to be processed with the same parameters as for example polyethylene. The presence of prooxidant in their composition ensures its oxo-destruction after the end of the product’s service life with the subsequent biodegradation of the obtained material fragments. The combination of a natural filler and a pro-oxidant additive in polymer compositions makes it possible to obtain a material with a programmed life and destruction
Thermal properties of polyethylene compositions with micro-and nanocellulose
Authors: Perova A N , Usachev S V , Koverzanova E V , Khvatov A V , Lomakin S M
Published: September 2020

The effect of micro- and nanocellulose addition on the thermal properties of polyethylene compositions has been studied by means of thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry. The main temperature characteristics of the thermo- and thermo-oxidative degradation of the compositions are determined. The influence of micro- and nanocellulose additives on change of the distribution of hydrocarbon pyrolysis products of composite materials was established.
Study of hydraulic resistance in collapsible pipelines
Authors: Seoev L V , Drozdov D A , Plotnikova K M , Elkin A V
Published: September 2020

The features of conducting research on hydraulic resistances of collapsible pipelines with a bell and spigot joint are shown. The importance of taking into account the influence of pipe joints on the flow of the pumped liquid, as well as deviations from straightness due to angular mobility, is noted. Data on the determination of pressure losses in collapsible pipelines PMTP-100 and TSR-MK-100 based on the results of tests carried out on sections of 1200 m long when pumping water are presented. The values of Darcy friction factor are also set. As a result of processing experimental data using mathematical statistics, the values of the coefficient of equivalent roughness of the inner surface of pipes of prefabricated pipelines PMTP-100 and TSR-MK-100 were determined. Using the methodological apparatus of hydraulic modeling, calculations were made to simulate the pumping of various groups and brands fuels through collapsible pipelines. In the analysis of the data revealed that by reducing the coefficient of equivalent roughness of the inner surface of pipes, supply pipeline TSR-MK-100 can be higher than by pipeline PMTP-100 on average, 5-13%.
Laser ablation method for the generation of chromium, iron, manganese, nickel, scandium, titanium and vanadium, nanoparticles: control of size and properties
Authors: Simakin Alexander V , Baimler Ilya V , Uvarov Oleg V , Rakov Ignat I , Gudkov Sergey V
Published: September 2020

Using method of laser ablation of massive targets in liquids, nanoparticles (NP) of chromium, iron, manganese, nickel, scandium, titanium and vanadium with controlled characteristics were generated. To generate NP with the desired characteristics, both ablation of macro-sized butt and fragmentation are consumed. Laser fragmentation is the process of melting large NP into small ones using laser radiation. The influence on the distribution of NP by diameter (size) of such key parameters of laser irradiation as the density of energy of beam of laser in the medium and power of the laser is determined. To obtain NP devoid of surface oxide films, organic solvents or water saturated with molecular hydrogen were used as a working fluid. The proposed approaches allow one to obtain NP that meet the following criteria: 1). the type of NP tends to be spherical; 2). 95% of NP have a certain radius; 3). NP consist of a single chemical element, the quantity of impurities is minimal; 4). the crystal lattice of NP is metallic. If necessary, it is possible to generate NP with a surface layer consisting from oxides, as well as fully oxidized NP.
Modeling of the development of the Vuktyl field hydrocarbon system in the depletion mode using a bench installation
Authors: Skibitskaya N.A. , Volkov A.N. , Latishev A.A. , Indrupsky I.M. , Popov A.A. , Bolshakov M.N. , Kuzmin V.A. , Marutyan O.O.
Published: September 2020

The work substantiates the location of liquid hydrocarbons (LH – oil and retrograde condensate) in the dynamic, filtering part of the capacitive volumes of gas-saturated productive deposits of gas condensate and oil and gas condensate fields (GCF and OGCF). The necessity of the development and bench modeling of the production of LH from gas-saturated deposits of GCF and OGCF in the late stages of field development is shown due to the high geological reserves of LH in them and the need to develop them with the aim of component recovery increasing and extending the life of the fields. The experience of bench modeling on the experimental installation of the life cycle of the oil and gas condensate system of the Vuktyl OGCF for the period of its development on the “depletion” mode is described. On the basis of a highly permeable core model, a simulation of the initial fluid saturation was successfully held which fits the initial state of the reservoir system of the Vuktyl OGCF, including the LC (reservoir oil), and also the current thermobaric state and fluid saturation of the reservoir system were simulated. The total mass of LH (reservoir oil and retrograde condensate) in the reservoir model is determined which can be taken as a basis for calculating the LH extraction rate while carrying out further research on bench modeling of LH production technologies in the late stages of Vuktil field development on the core model created. As a result of the works described above, an oil and gas condensate system was created in a highly permeable bench core model which is the model of depleted to maximum condensation pressure reservoir of Vuktyl OGCF.
Chemical stability of modern jet fuels
Authors: Vlasenkova L A , Shatalov K V , Likhterova N M
Published: September 2020

The article shows the need to study the chemical stability of jet engine fuels containing components of deep oil refining and offers a method for studying the chemical stability of jet engine fuels. Based on this method, research was conducted on jet engine fuels of various production technologies and the influence of the hydrocarbon composition on the chemical stability of a mixture of individual hydrocarbons was studied. The inhibitory effect of aromatic hydrocarbons in a mixture with different content of naphthenic hydrocarbons has been studied. Using artificial aging of jet engine fuels, a low level of chemical stability of jet engine fuels based on hydrocracking of vacuum oil strips is shown.
Purification of hydrocarbon-contaminated soils by silicon-rich substances
Authors: Wei X , Matichenkov V V , Bocharnikova E A , Sevostianov S M
Published: September 2020

Hydrocarbon (HC) contamination of soil occurs during oil extraction, transportation and treatment. To enhance the efficacy of HC-polluted soil restoration is an important challenge. In greenhouse and field experiments, two silicon (Si)-rich substances were tested for reduction of HC content in diesel + used motor oil contaminated soil. Over 3 months the HC content decreased from 3 to 2.8; 1.1 and 0.8% in control, calcium silicate slag- and amorphous Si dioxide-treated soils, respectively. Silicon-rich substances remarkably increased the catalase and dehydrogenase activities in the contaminated soil. Several mechanisms underlying the Si-mediated purification of HC-contaminated soil are suggested: a) changing soil physical properties; b) capsulation of HC molecules by polysilicic acid; c) adsorption of monosilicic acid by HCs leading to enhanced hydrophilicity; d) direct effect on soil microbial activity. Many types of Si-rich materials are cheap and available in large volumes (industrial by-products) that potentially could be used for the purification of HC-polluted environment after ecological expertise of the absence of inorganic pollutants.
PbO2decorated ZnO-TiO2core-shell nanoflower structures by zinc anodising for photo- and anodic degradation of Reactive Black-5 dye
Authors: Harito Christian , Zaidi Syed Z.J. , Bavykin Dmitry V. , Martins Alysson S. , Yuliarto Brian , Walsh Frank C. , de León Carlos Ponce
Published: September 2020

This work shows that metallic zinc can be used as a low-cost substrate or electrode for photocatalyst and electrocatalyst use by anodising in mild bicarbonate solution. Electrochemical anodising was used to produce ZnO nanowires by controlling operational conditions and dip-coating the anodised surface with TiO2to produce a core-shell coating with photocatalytic properties. The PbO2,which is known as good electrocatalyst, was electrodeposited over the ZnO-TiO2core-shell structure to alter its surface for electrocatalytic degradation of dye. The electrochemical and photocatalytic behaviours of the coatings were analysed for the removal of RB-5 dye as model pollutant. For the ZnO-TiO2core-shell, the photocatalytic removal mechanism was driven by the heterojunction photocatalytic effect of photocatalytically active anatase TiO2and wurtzite ZnO. Photocatalysis was switched to electrocatalytic behaviour after incorporation of PbO2.Although the UV light might be blocked by PbO2, the electrochemical degradation was enhanced due to the creation of·OH free radicals over the PbO2particles decorating a ZnO-TiO2core-shell composite coating.
Pulse shape discrimination and exploration of scintillation signals using convolutional neural networks
Authors: Griffiths J , Kleinegesse S , Saunders D , Taylor R , Vacheret A
Published: September 2020

We demonstrate the use of a convolutional neural network to perform neutron-gamma pulse shape discrimination, where the only inputs to the network are the raw digitised silicon photomultiplier signals from a dual scintillator detector element made of 6Li F:ZnS(Ag) scintillator and PVT plastic. A realistic labelled dataset was created to train the network by exposing the detector to an AmBe source, and a data-driven method utilising a separate photomultiplier tube was used to assign labels to the recorded signals. This approach is compared to the charge integration and continuous wavelet transform methods and a simpler artificial neural net. It is found to provide superior levels of discrimination, achieving an area under the curve of 0.996 ± 0.003. We find that the neural network is capable of extracting interpretable features directly from the raw data. In addition, by visualising the high-dimensional representations of the network with the t-SNE algorithm, we discover that not only is this method robust to minor mislabeling of the training dataset but that it is possible to identify an underlying substructure within the signals that goes beyond the original labelling. This technique could be utilised to explore and cluster complex, raw detector data in a novel way that may reveal more insights than standard analysis methods.
The political economy of Biafra separatism and post-war Igbo nationalism in Nigeria
Authors: Nwangwu Chikodiri , Onuoha Freedom C , Nwosu Bernard U , Ezeibe Christian
Published: September 2020

The past two decades that coincide with the return of civil rule in most African countries have witnessed the reinforcement of ethnic nationalism and separatist agitations. While scholarly attention has focused on ethnicity to explain the revival of ethnic nationalism, how ethnic and class discourses conflate in the pursuit of ethnic nationalism remains understudied. Using a qualitative-dominant approach, this article interrogates how the Igbo petty bourgeoisie use ethnicity to mask the underlying differences in their material conditions in relation to the alienated masses. It also examines how these differences shape post-war Igbo nationalism. In the main, this article argues that the intersection of ethnic and class discourses is underpinned by unequal distribution of rights and powers accruing from productive resources. This unequal distribution of rights and powers results in differential material well-being and gives rise to conflicts between the dominant and subordinate classes. This explains the divergent approaches of the different factions of Igbo petty bourgeoisie to Igbo nationalism in Nigeria. The article concludes that understanding the political economy of the intersection of ethnic and class discourses is relevant for resolving the nationality question and the Biafra secessionist agitations in Nigeria and others across Africa.
Adversarial deconfounding autoencoder for learning robust gene expression embeddings
Authors: Dincer Ayse B , Janizek Joseph D , Lee Su-In
Published: September 2020

Motivation

Increasing number of gene expression profiles has enabled the use of complex models, such as deep unsupervised neural networks, to extract a latent space from these profiles. However, expression profiles, especially when collected in large numbers, inherently contain variations introduced by technical artifacts (e.g. batch effects) and uninteresting biological variables (e.g. age) in addition to the true signals of interest. These sources of variations, called confounders, produce embeddings that fail to transfer to different domains, i.e. an embedding learned from one dataset with a specific confounder distribution does not generalize to different distributions. To remedy this problem, we attempt to disentangle confounders from true signals to generate biologically informative embeddings.

Results

In this article, we introduce the Adversarial Deconfounding AutoEncoder (AD-AE) approach to deconfounding gene expression latent spaces. The AD-AE model consists of two neural networks: (i) an autoencoder to generate an embedding that can reconstruct original measurements, and (ii) an adversary trained to predict the confounder from that embedding. We jointly train the networks to generate embeddings that can encode as much information as possible without encoding any confounding signal. By applying AD-AE to two distinct gene expression datasets, we show that our model can (i) generate embeddings that do not encode confounder information, (ii) conserve the biological signals present in the original space and (iii) generalize successfully across different confounder domains. We demonstrate that AD-AE outperforms standard autoencoder and other deconfounding approaches.

Availability and implementation

Our code and data are available at https://gitlab.cs.washington.edu/abdincer/ad-ae.

Contact

Supplementary information

Supplementary data are available at Bioinformatics online.
PBSIM2: a simulator for long-read sequencers with a novel generative model of quality scores
Authors: Ono Yukiteru , Asai Kiyoshi , Hamada Michiaki
Published: September 2020

Motivation

Recent advances in high-throughput long-read sequencers, such as PacBio and Oxford Nanopore sequencers, produce longer reads with more errors than short-read sequencers. In addition to the high error rates of reads, non-uniformity of errors leads to difficulties in various downstream analyses using long reads. Many useful simulators, which characterize long-read error patterns and simulate them, have been developed. However, there is still room for improvement in the simulation of the non-uniformity of errors.

Results

To capture characteristics of errors in reads for long-read sequencers, here, we introduce a generative model for quality scores, in which a hidden Markov Model with a latest model selection method, called factorized information criteria, is utilized. We evaluated our developed simulator from various points, indicating that our simulator successfully simulates reads that are consistent with real reads.

Availability and implementation

The source codes of PBSIM2 are freely available from https://github.com/yukiteruono/pbsim2.

Supplementary information

Supplementary data are available at Bioinformatics online.
Mortality and Prognostic Factors of Nontuberculous Mycobacterial Infection in Korea: A Population-based Comparative Study
Authors: Lee Hyewon , Myung Woojae , Lee Eun-Mi , Kim Hyekyeong , Jhun Byung Woo
Published: September 2020

Background

Population-based studies on the mortality burden of nontuberculous mycobacteria (NTM) infection are lacking. We compared the long-term mortality of NTM-infected patients with tuberculosis (TB)-patients and the general population, and investigated mortality-associated factors.

Methods

We analyzed nationwide-data from the Korean National Health Insurance and Korea-Statistical Office between 2002 and 2017. NTM infection was identified using the International Classification of Disease, Tenth Revision code, with one-to-one matching to TB patients and general population controls.

Results

A total of 530 401 individuals were analyzed, including 183 267 with NTM infections; 166 666 with TB; and 180 468 controls. The overall 6-, 10-, and 14-year cumulative survival probabilities in the NTM group were 86.3%, 80.8%, and 77.1%, respectively, which were significantly lower than those of the TB or control groups (log-rank P < .0001). In cases of NTM and TB coinfection, the overall 6-, 10-, and 14-year cumulative survival probabilities were 75.1%, 65.4%, and 57.0%, respectively. Multivariable analysis indicated that old age, male gender, province, and various respiratory or nonrespiratory comorbidities were significantly associated with mortality of NTM infection. The use of a macrolide (more than 1 year) negatively correlated with mortality of NTM infection (adjusted hazard ratio [aHR] 0.61, 95% confidence interval [CI] .53–.71), regardless of azithromycin (aHR 0.60, 95% CI .43–.85) or clarithromycin use (aHR 0.63, 95% CI .53–.75).

Conclusions

NTM-infected patients had poor prognosis when compared to TB patients or the general population, especially for NTM and TB coinfection. NTM mortality was associated with certain demographic characteristics, but long-term use of macrolides may provide survival benefits.
Kinetics of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Antibody Avidity Maturation and Association with Disease Severity
Authors: Luo Yiqi Ruben , Chakraborty Indrani , Yun Cassandra , Wu Alan H B , Lynch Kara L
Published: September 2020

The kinetics of IgG avidity maturation during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was studied. The IgG avidity assay, using a novel label-free immunoassay technology, revealed a strong correlation between IgG avidity and days since symptom onset. Peak readings were significantly higher in severe than mild disease cases.
An aortic root abscess in a patient with a bicuspid aortic valve: a case report
Authors: Balzan Elyse , Borg Alexander
Published: September 2020

Background

Infective endocarditis is a serious infection associated with high mortality and severe complications, such as heart failure, uncontrolled infection, and embolic events. Certain populations, including individuals with a prosthetic valve and those with native valve disease, such as bicuspid aortic valve, are considered to be more at risk of developing infective endocarditis.

Case summary

A 51-year-old previously healthy male presented with a 2-week history of persistent fever, malaise, and night sweats despite taking a long course of oral antibiotics. Examination was unremarkable; however, blood tests showed elevated inflammatory markers. Three sets of blood cultures revealed coagulase-negative gram-positive cocci (later identified as Staphylococcus lugdunensis), and the patient was subsequently started on IV antibiotics. His echocardiography showed a bicuspid aortic valve with severe regurgitation, and an aortic root abscess surrounding a dilated aortic root. In view of the presence of locally uncontrolled infection, the patient was referred for urgent debridement of the abscess and replacement of the aortic valve with tissue prosthesis. Fortunately, after a total of 6 weeks of IV antibiotics and successful operative management, our patient made a complete recovery.

Discussion

The development of an aortic root abscess occurs in 10–40% of cases of aortic valve endocarditis. Clinically, this should be suspected in any patient with endocarditis who fails to improve despite appropriate antibiotic therapy. This case demonstrates that severe infective endocarditis can develop in apparently healthy individuals due to underlying cardiac abnormalities.
Nonesterified Fatty Acids and Hospitalizations Among Older Adults: The Cardiovascular Health Study
Authors: Ahiawodzi Peter D , Buzkova Petra , Djousse Luc , Ix Joachim H , Kizer Jorge R , Mukamal Kenneth J
Published: September 2020

Background

We sought to determine associations between total serum concentrations of nonesterified fatty acids (NEFAs) and incident total and cause-specific hospitalizations in a community-living cohort of older adults.

Methods

We included 4715 participants in the Cardiovascular Health Study who had fasting total serum NEFA measured at the 1992/1993 clinic visit and were followed for a median of 12 years. We identified all inpatient admissions requiring at least an overnight hospitalization and used primary diagnostic codes to categorize cause-specific hospitalizations. We used Cox proportional hazards regression models to determine associations with time-to-first hospitalization and Poisson regression for the rate ratios (RRs) of hospitalizations and days hospitalized.

Results

We identified 21 339 hospitalizations during follow-up. In fully adjusted models, higher total NEFAs were significantly associated with higher risk of incident hospitalization (hazard ratio [HR] per SD [0.2 mEq/L] = 1.07, 95% confidence interval [CI] = 1.03–1.10, p < .001), number of hospitalizations (RR per SD = 1.04, 95% CI = 1.01–1.07, p = .01), and total number of days hospitalized (RR per SD = 1.06, 95% CI = 1.01–1.10, p = .01). Among hospitalization subtypes, higher NEFA was associated with higher likelihood of mental, neurologic, respiratory, and musculoskeletal causes of hospitalization. Among specific causes of hospitalization, higher NEFA was associated with diabetes, pneumonia, and gastrointestinal hemorrhage.

Conclusions

Higher fasting total serum NEFAs are associated with a broad array of causes of hospitalization among older adults. While some of these were expected, our results illustrate a possible utility of NEFAs as biomarkers for risk of hospitalization, and total days hospitalized, in older adults. Further research is needed to determine whether interventions based on NEFAs might be feasible.
Demographic and Socioeconomic Disparities in Life Expectancy With Hearing Impairment in the United States
Authors: West Jessica S , Lynch Scott M
Published: September 2020

Objectives

Hearing impairment is one of the most common disabilities among older people, and its prevalence will increase as the U.S. population ages. However, little is known about social disparities in onset or transitions into and out of hearing impairment, nor how these transitions impact years of life to be spent impaired.

Method

We investigate the number of years an “average” person can expect to live with and without hearing impairment after age 50; sex, race, educational, and regional differences in these expectancies; and the implication of hearing impairment for remaining life expectancy. Bayesian multistate life table methods are applied to 9 waves of data from the Health and Retirement Study (1998–2014) to investigate social disparities in life expectancy with hearing impairment (n = 20,200) for the general population, people hearing impaired at age 50, and people hearing unimpaired at age 50.

Results

Men, Hispanics, persons with less educational attainment, and those born in the south can expect to live a larger proportion of their remaining lives hearing impaired. Although transitions from hearing impaired to unimpaired occur, those with some hearing impairment at age 50 can expect to live more years with hearing impairment, and hearing impairment does not shorten remaining life expectancy.

Discussion

Significant sociodemographic disparities in hearing impaired life expectancy exist. In contrast to past research, we find that hearing impairment does not affect total life expectancy. Future research should consider the consequences of hearing impairment for years to be lived with other age-related and potentially downstream health outcomes.
Debt Stress and Debt Illusion: The Role of Consumer Credit, Reverse and Standard Mortgages
Authors: Haurin Donald R , Moulton Stephanie , Loibl Cäzilia , Brown Julia K
Published: September 2020

Objectives

This study examines the relationship of debt stress and reverse mortgage borrowing and compares it to stress from standard mortgages and consumer debt. Debt stress is measured as a self-reported response to the amount of debt.

Methods

Using a unique national data set of 1,026 homeowners who chose whether to obtain a reverse mortgage in 2010, we estimate the relationship of 2014 levels of debt stress with various types of debt, assets, and income. Using an ordered probit model, we address the endogeneity of our measures of mortgage and consumer debt using an instrumental variables regression model.

Results

We found that consumer debt causes more stress per dollar of debt compared to mortgage debt. Reverse mortgages cause a relatively low level of stress per dollar of debt compared with standard mortgage debt. The average treatment effect of originating a reverse mortgage indicates statistically significantly higher probability of reporting no and not very much debt stress.

Discussion

Reverse mortgage debt causes a complex stress response. Stress per dollar of debt is lower for reverse than standard mortgages 4 years after origination. However, reverse mortgages’ loan balance grows over time causing total stress to increase, while stress from a standard mortgage decreases as it is repaid. If an older adult uses reverse mortgage funds to repay consumer debt then total stress is reduced.