bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Machinability of the Inconel 718 Superalloy during the Electrical Discharge Drilling Process
Authors: Machno Magdalena
Published: August 2020

The properties of the Inconel 718 superalloy are used in the manufacturing of aircraft components; its properties, including high hardness and toughness, cause machining difficulties when using the conventional method. To circumvent this, non-conventional techniques are used, among which electrical discharge machining (EDM) is a good alternative. However, the nature of removing material using the EDM process causes the thermophysical properties of Inconel 718 to hinder its machinability; thus, a more extensive analysis of the influence of these properties on the EDM process, and a machinability analysis of this material in a wider range, using more process parameters, are required. In this study, we investigated the drilling of micro-holes into the Inconel 718 superalloy using the EDM process. An experiment was conducted to evaluate the impact of five process parameters with a wide range of values (open voltage, time of the impulse, current amplitude, the inlet dielectric fluid pressure, and tube electrode rotation) on the process’s performance (drilling speed, linear tool wear, the side gap thickness, and the aspect ratio of holes). The analysis shows that the thermal conductivity of this superalloy significantly influences the effective drilling of holes. The combination of a higher current amplitude (I ≥ 3.99 A) with an extended pulse time (ton ≥ 550 µs) can provide a satisfactory hole accuracy (side gap thickness ≤ 100 µm), homogeneity of the hole entrance edge without re-solidified material, and a depth-to-diameter ratio of about 19. Obtaining a high dimensional shape accuracy of holes has an enormous effect on their usability in the structure of the components in the aviation industry.
Native Bovine Hydroxyapatite Powder, Demineralised Bone Matrix Powder, and Purified Bone Collagen Membranes Are Efficient in Repair of Critical-Sized Rat Calvarial Defects
Authors: Veremeev Alexey , Bolgarin Roman , Nesterenko Vladimir , Andreev-Andrievskiy Alexander , Kutikhin Anton
Published: August 2020

Here we evaluated the efficacy of bone repair using various native bovine biomaterials (refined hydroxyapatite (HA), demineralised bone matrix (DBM), and purified bone collagen (COLL)) as compared with commercially available bone mineral and bone autografts. We employed a conventional critical-sized (8 mm diameter) rat calvarial defect model (6-month-old male Sprague–Dawley rats, n = 72 in total). The artificial defect was repaired using HA, DBM, COLL, commercially available bone mineral powder, bone calvarial autograft, or remained unfilled (n = 12 animals per group). Rats were euthanised 4 or 12 weeks postimplantation (n = 6 per time point) with the subsequent examination to assess the extent, volume, area, and mineral density of the repaired tissue by means of microcomputed tomography and hematoxylin and eosin staining. Bovine HA and DBM powder exhibited excellent repair capability similar to the autografts and commercially available bone mineral powder while COLL showed higher bone repair rate. We suggest that HA and DBM powder obtained from bovine bone tissue can be equally applied for the repair of bone defects and demonstrate sufficient potential to be implemented into clinical studies.
Efficiency of Plasticity Correction in the Hole-Drilling Residual Stress Measurement
Authors: Návrat Tomáš , Halabuk Dávid , Vosynek Petr
Published: August 2020

This paper focuses on the analysis of the plasticity effect in the measurement of the residual stress by the hole-drilling method. Relaxed strains were evaluated by the computational simulation of the hole-drilling experiment using the finite element method. Errors induced by the yielding were estimated for uniaxial tension, plane shear stress state and equi-biaxial stress state at various magnitudes of residual stress uniformly distributed along the depth. The correction of the plasticity effect in the evaluation of residual stress was realized according to the method proposed by authors from the University in Pisa, which was coded in MATLAB. Results obtained from the MATLAB script were compared to the original input data of the hole-drilling simulation and discussed. The analyses suggested that the plasticity effect is negligible at the ratio of applied equivalent stress to yield stress, being 0.6, and that the correction of the plasticity effect is very successful at the previous ratio, being 0.9. Failing to comply with the condition of the strain gauge rosette orientation according to the principal stresses directions causes an increase in the relative error of corrected stresses only for the case of uniaxial tension. It affects the relative error negligibly for the plane shear and equi-biaxial stress states.
Gd3+-Doping Effect on Upconversion Emission of NaYF4: Yb3+, Er3+/Tm3+ Microparticles
Authors: Vidyakina Aleksandra A. , Kolesnikov Ilya E. , Bogachev Nikita A. , Skripkin Mikhail Y. , Tumkin Ilya I. , Lähderanta Erkki , Mereshchenko Andrey S.
Published: August 2020

β-NaYF4 microcrystals co-doped with Yb3+, Er3+/Tm3+, and Gd3+ ions were synthesized via a hydrothermal method using rare-earth chlorides as the precursors. The SEM and XRD data show that the doped β-NaYF4 form uniform hexagonal prisms with an approximate size of 600–800 nm. The partial substitution of Y by Gd results in size reduction of microcrystals. Upconversion luminescence spectra of microcrystals upon 980 nm excitation contain characteristic intra-configurational ff bands of Er3+/Tm3+ ions. An addition of Gd3+ ions leads to a significant enhancement of upconversion luminescence intensity with maxima at 5 mol % of dopant.
Selective Partial Hydrolysis of 2-isopropyl-2-oxazoline Copolymers towards Decreasing the Ability to Crystallize
Authors: Oleszko-Torbus Natalia , Mendrek Barbara , Kowalczuk Agnieszka , Utrata-Wesołek Alicja , Dworak Andrzej , Wałach Wojciech
Published: August 2020

Poly(2-isopropyl-2-oxazoline) (PiPrOx) is readily prone to crystallization both in solid and from solutions. This feature is detrimental for certain applications. Here, we examine whether the presence of unsubstituted ethyleneimine (EI) units, a gradient distributed within a polymer chain composed of 2-isopropyl-2-oxazoline (iPrOx) and 2-methyl-2-oxazoline (MOx) units, decreases the ability to crystallize the copolymer and affects thermal properties compared to the homopolymer of iPrOx. We assumed that the separation of stiff iPrOx units by the more flexible EI will affect the spatial arrangements of the ordered chains, slightly plasticize and, as a result, decrease their ability to crystallize. The selective hydrolysis of gradient iPrOx and 2-methyl-2-oxazoline (MOx) copolymers, carried out under mild conditions, led to iPrOx/MOx/EI copolymers. To the best of our knowledge, the selective hydrolysis of these copolymers has never been carried out before. Their thermal properties and crystallization abilities, both in a solid state and from an aqueous solution, were analyzed. Based on the analysis of polymer charge and cytotoxicity studies, the potential use of the copolymers obtained was indicated in some biological systems.
Slag Blended Cement Paste Carbonation under Different CO2 Concentrations: Controls on Mineralogy and Morphology of Products
Authors: Liu Wei , Lin Shifa , Li Yongqiang , Long Wujian , Dong Zhijun , Tang Luping
Published: August 2020

To investigate the effect of different CO2 concentrations on the carbonation results of slag blended cement pastes, carbonation experiments under natural (0.03% CO2) and accelerated conditions (3, 20, and 100% CO2) were investigated with various microscopic testing methods, including X-ray diffraction (XRD), 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) and scanning electron microscopy (SEM). The XRD results indicated that the major polymorphs of CaCO3 after carbonation were calcite and vaterite. The values of the calcite/(aragonite + vaterite) (c/(a + v)) ratios were almost the same in all carbonation conditions. Additionally, NMR results showed that the decalcification degree of C-S-H gel exposed to 0.03% CO2 was less than that exposed to accelerated carbonation; under accelerated conditions, it increased from 83.1 to 84.2% when the CO2 concentration improved from 3% to 100%. In SEM observations, the microstructures after accelerated carbonation were denser than those under natural carbonation but showed minor differences between different CO2 concentrations. In conclusion, for cement pastes blended with 20% slag, a higher CO2 concentration (above 3%) led to products different from those produced under natural carbonation. A further increase in CO2 concentration showed limited variation in generated carbonation products.
Performance of Maraging Steel Sleeves Produced by SLM with Subsequent Age Hardening
Authors: Tyczyński Piotr , Siemiątkowski Zbigniew , Bąk Piotr , Warzocha Krzysztof , Rucki Mirosław , Szumiata Tadeusz
Published: August 2020

In the paper, the researches on sleeves made out of maraging steel 1.2709 using selective laser melting (SLM) technology are presented. This additive technology is recognized as favorable for the environment, due to 100% use of material and durability of manufactured details. The fabricated sleeves underwent subsequent tests, in particular, microhardness, porosity and homogeneity of the material was examined before and after heat treatment and salt bath nitrocarburizing process. Two kinds of fatigue tests were performed. The first consisted of the typical sinusoidal alternating load, the other was the high pressure pulse load test close to the real work conditions. It is of high importance that the fatigue strength of the tested sleeves is considerably higher than that of the similarly produced details shaped as a standard samples for tensile stress. The Mössbauer spectrometry analysis of hyperfine magnetic field distributions proved that SLM did not change considerably the martensite structure at atomic level.
Synthesis and Antibacterial Activity of (AgCl, Ag)NPs/Diatomite Hybrid Composite
Authors: Kubasheva Zhanar , Sprynskyy Myroslav , Railean-Plugaru Viorica , Pomastowski Paweł , Ospanova Aliya , Buszewski Bogusław
Published: August 2020

In the present research, hybrid (AgCl, Ag)NPs/diatomite composites were synthesized by direct impregnation with aqueous silver nitrate solutions. The silver chloride nanoparticles (AgCl-NPs) were formed as an effect of the exchange reaction when silver interacted with the diatomite mineral impurity halite. Nanoparticles of metallic silver (AgNPs) were created by the reduction of silver ions under the influence of hydrogen peroxide. The content of silver chloride nanoparticles in the (AgCl, Ag)NPs/diatomite composite was limited by the content of the halite in the used diatomite. Samples of natural diatomite and synthesized (AgCl, Ag)NPs/diatomite composites were examined by using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, infrared spectroscopy and thermogravimetric analysis. Moreover, the antibacterial potential of synthesized composites was also studied using the MIC (minimal inhibitory concentration) method against the most common drug-resistant microorganisms in the medical field: Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae. The obtained hybrid (AgCl, AgNPs)/diatomite composites were shown to have antimicrobial potential. However, widespread use requires further study by using various microorganisms and additional cytotoxic studies on eukaryotic systems, e.g., cell lines and animal models.
Investigation on Surface Quality of a Rapidly Solidified Al–50%Si Alloy Component for Deep-Space Applications
Authors: Chaieb Oussama , Olufayo Oluwole A. , Songmene Victor , Jahazi Mohammad
Published: August 2020

To meet the requirements for high-performance products, the aerospace industry increasingly needs to assess the behavior of new and advanced materials during manufacturing processes and to ensure they possess adequate machinability, as well as high performance and an extensive lifecycles. Over the years, industrial research works have focused on developing new alloys with an increased thermal conductivity as well as increased strength. High silicon content aluminum (Al–Si) alloys, due to their increased thermal conductivity, low coefficient of thermal expansion, and low density, have been identified as suitable materials for space applications. Some of these applications require the use of intricate parts with tight tolerances and surface integrity. These challenges are often tied to the machining conditions and strategies, as well as to workpiece materials. In this study, experimental milling tests were performed on a rapidly solidified (RS) Al–Si alloy with a prominent silicon content (over 50%) to address challenges linked to material expansion in deep space applications. The tests were performed using a polycrystalline cubic boron nitride (PCBN) tool coated with amorphous diamond to reduce tool wear, material adhesion, surface oxidation, and particle diffusion. The effects of cutting parameters on part surface roughness and microstructure were analyzed. A comparative analysis of the surface with a conventionally utilized Al6061-T6 alloy showed an improvement in surface roughness measurements when using the RS Al–Si alloy. The results indicated that lower cutting speed and feed rate on both conventional and RS Al–Si alloys produced a better surface finish. Reduced vibrations were also identified in the RS Al–Si alloy, which possessed a stable cutting time at low cutting speeds but only displayed notable vibrations at cutting speeds above 120 m/min.
Recent Advances and Trends of Nanofilled/Nanostructured Epoxies
Authors: Frigione Mariaenrica , Lettieri Mariateresa
Published: August 2020

This paper aims at reviewing the works published in the last five years (2016–2020) on polymer nanocomposites based on epoxy resins. The different nanofillers successfully added to epoxies to enhance some of their characteristics, in relation to the nature and the feature of each nanofiller, are illustrated. The organic–inorganic hybrid nanostructured epoxies are also introduced and their strong potential in many applications has been highlighted. The different methods and routes employed for the production of nanofilled/nanostructured epoxies are described. A discussion of the main properties and final performance, which comprise durability, of epoxy nanocomposites, depending on chemical nature, shape, and size of nanoparticles and on their distribution, is presented. It is also shown why an efficient uniform dispersion of the nanofillers in the epoxy matrix, along with strong interfacial interactions with the polymeric network, will guarantee the success of the application for which the nanocomposite is proposed. The mechanisms yielding to the improved properties in comparison to the neat polymer are illustrated. The most important applications in which these new materials can better exploit their uniqueness are finally presented, also evidencing the aspects that limit a wider diffusion.
Investigating the Response of Human Neutrophils to Hydrophilic and Hydrophobic Micro-Rough Titanium Surfaces
Authors: El Kholy Karim , Buser Daniel , Wittneben Julia-Gabriella , Bosshardt Dieter D. , Van Dyke Thomas E. , Kowolik Michael J.
Published: August 2020

Various treatments have been used to change both the topography and chemistry of titanium surfaces, aiming to enhance tissue response and reduce healing times of endosseous implants. Most studies to date focused on bone healing around dental implants occurring later during the healing cascade. However, the impact of the initial inflammatory response in the surgical wound site on the success and healing time of dental implants is crucial for implant integration and success, yet it is still poorly understood. The purpose of this study was to investigate the effect of titanium surface hydrophilicity on the response of human neutrophils by monitoring oxygen radical production, which was measured as chemiluminescence activity. Materials and Methods: Neutrophils were isolated from human donors’ blood buffy coats using the double sucrose gradient method. Neutrophils were exposed to both hydrophilic and hydrophobic titanium surfaces with identical topographies in the presence and absence of human serum. This resulted in six experimental groups including two different implant surfaces, with and without exposure to human serum, and two control groups including an active control with cells alone and a passive control with no cells. Two samples from each group were fixed and analyzed by SEM. Comparisons between surface treatments for differences in chemiluminescence values were performed using analysis of variance ANOVA. Results and Conclusion: In the absence of exposure to serum, there was no significant difference noted between the reaction of neutrophils to hydrophilic and hydrophobic surfaces. However, there was a significant reduction in the mean and active chemiluminescence activity of neutrophils to serum-coated hydrophilic titanium surfaces than to serum-coated hydrophobic titanium surfaces. This suggests that surface hydrophilicity promotes enhanced adsorption of serum proteins, which leads to decreased provocation of initial immune cells and reduction of local oxygen radical production during wound healing. This can help explain the faster osseointegration demonstrated by hydrophilic titanium implants.
Torsional Behaviour of Steel Fibre Reinforced Alkali Activated Concrete
Authors: Lau Chee Keong , Htut Trevor N. S. , Melling Jack J. , Chegenizadeh Amin , Ng Tian Sing
Published: August 2020

Nine alkali-activated concrete beams were produced and tested under pure torsional load to failure. The alkali-activated concrete beams were produced with following variables: (i) fibres only, (ii) conventionally reinforced or (iii) a hybrid of both fibres and conventional steel reinforcement. The fibres only beams were found to have approximately 20% higher cracking torque than conventionally reinforced beams. However, fibres only beams were observed to have lower post crack ductility and inconsistent post crack behaviour, in comparison to conventionally reinforced alkali-activated concrete (AAC) beams. On the other hand, the hybrid reinforcements in AAC beams were found to demonstrate more ductile post crack behaviour consistently of the beams tested. Hybrid reinforcement was also shown to have 20% and 25% improvement in cracking and ultimate torque compared to conventionally reinforced, which suggests that it is suitable for industrial applications to improve structure capacity. The ultimate torque results of the beams were compared to an analytical model that considered the contribution of fibres. It was found that the ultimate torque of the hybrid reinforced beam has good correlation with the model but overestimated conventionally reinforced beams.
Constitutive Equations for Describing the Hot Compressed Behavior of TC4–DT Titanium Alloy
Authors: Wang Haoran , Wang Chunge , Li Muyu , Ma Rui , Zhao Jun
Published: August 2020

Isothermal hot compression tests of TC4–DT titanium alloy were performed under temperatures of 1203–1293 K and strain rates of 0.001–10 s−1. The purpose of this study is to develop a new high-precision modified constitutive model that can describe the deformation behavior of TC4–DT titanium alloy. Both the modified strain-compensated Arrhenius-type equation and the modified Hensel–Spittel equation were established by revising the strain rate. The parameters in the above two modified constitutive equation were solved by combining regression analysis with iterative methods, which was used instead on the traditional linear regression methods. In addition, both the original strain-compensated Arrhenius-type equation and Hensel–Spittel equation were established to compare with the new modified constitutive equations. A comparison of the predicted values based on the four constitutive equations was performed via relative error, average absolute relative error (AARE) and the correlation coefficient (R). These results show the modified Arrhenius-type equation and the modified Hensel–Spittel equation is more accurate and efficient with a similar prediction accuracy. The AARE-value of the two modified constitutive equation is relatively low under various strain rates and their fluctuation is small as the strain rate changes.
Influence of Backing Plate Support Conditions on Armor Ceramic Protection Efficiency
Authors: Zhang Bowen , Wang Yangwei , Du Shaofeng , Yang Zhikun , Cheng Huanwu , Fan Qunbo
Published: August 2020

The bilayer composite ceramic armor is widely used in the world, while the protection efficiency of the armor ceramic in it still confuses researchers. This study applied a numerical simulation method to produce a general equation that describes the relationship between the protection efficiency of the armor ceramic and the supporting conditions of the backing plate, thereby enhancing the current understanding of the composite ceramic armor. The results indicated that the protection efficiency of the armor ceramic can be divided into three parts: (1) the basic protection efficiency, (2) the increment efficiency caused by inertial support, and (3) the increment efficiency caused by mechanical support. The inertial support is related to the density and thickness of the backing plate, and the mechanical support is related to the elastic modulus and yield strength of the backing plate materials. The inertial support exhibited a positive correlation with the protection efficiency of the armor ceramic before it reached the Scr; after that, the protection efficiency of the armor ceramic would remain stable. In addition, the mechanical support showed a linear, positive correlation with the backing plate stress at ε0.
Anomalous Pressure Effects on the Electrical Conductivity of the Spin Crossover Complex [Fe(pyrazine){Au(CN)2}2]
Authors: Gheorghe Andrei-Cristian , Bibik Yurii S. , Kucheriv Olesia I. , Barakhtii Diana D. , Boicu Marin-Vlad , Rusu Ionela , Diaconu Andrei , Gural’skiy Il’ya A. , Molnár Gábor , Rotaru Aurelian
Published: August 2020

We studied the spin-state dependence of the electrical conductivity of two nanocrystalline powder samples of the spin crossover complex [Fe(pyrazine){Au(CN)2}2]. By applying an external pressure (up to 3 kbar), we were able to tune the charge transport properties of the material from a more conductive low spin state to a crossover point toward a more conductive high spin state. We rationalize these results by taking into account the spin-state dependence of the activation parameters of the conductivity.
On Semi-Classical Orthogonal Polynomials Associated with a Modified Sextic Freud-Type Weight
Authors: Kelil Abey S. , Appadu Appanah R.
Published: August 2020

Polynomials that are orthogonal with respect to a perturbation of the Freud weight function by some parameter, known to be modified Freudian orthogonal polynomials, are considered. In this contribution, we investigate certain properties of semi-classical modified Freud-type polynomials in which their corresponding semi-classical weight function is a more general deformation of the classical scaled sextic Freud weight |x|αexp(−cx6),c>0,α>−1. Certain characterizing properties of these polynomials such as moments, recurrence coefficients, holonomic equations that they satisfy, and certain non-linear differential-recurrence equations satisfied by the recurrence coefficients, using compatibility conditions for ladder operators for these orthogonal polynomials, are investigated. Differential-difference equations were also obtained via Shohat’s quasi-orthogonality approach and also second-order linear ODEs (with rational coefficients) satisfied by these polynomials. Modified Freudian polynomials can also be obtained via Chihara’s symmetrization process from the generalized Airy-type polynomials. The obtained linear differential equation plays an essential role in the electrostatic interpretation for the distribution of zeros of the corresponding Freudian polynomials.
Mobile Robot Wall-Following Control Using Fuzzy Logic Controller with Improved Differential Search and Reinforcement Learning
Authors: Chen Cheng-Hung , Jeng Shiou-Yun , Lin Cheng-Jian
Published: August 2020

In this study, a fuzzy logic controller with the reinforcement improved differential search algorithm (FLC_R-IDS) is proposed for solving a mobile robot wall-following control problem. This study uses the reward and punishment mechanisms of reinforcement learning to train the mobile robot wall-following control. The proposed improved differential search algorithm uses parameter adaptation to adjust the control parameters. To improve the exploration of the algorithm, a change in the number of superorganisms is required as it involves a stopover site. This study uses reinforcement learning to guide the behavior of the robot. When the mobile robot satisfies three reward conditions, it gets reward +1. The accumulated reward value is used to evaluate the controller and to replace the next controller training. Experimental results show that, compared with the traditional differential search algorithm and the chaos differential search algorithm, the average error value of the proposed FLC_R-IDS in the three experimental environments is reduced by 12.44%, 22.54% and 25.98%, respectively. Final, the experimental results also show that the real mobile robot using the proposed method can effectively implement the wall-following control.
A Robust Algorithm for Classification and Diagnosis of Brain Disease Using Local Linear Approximation and Generalized Autoregressive Conditional Heteroscedasticity Model
Authors: Hamzenejad Ali , Jafarzadeh Ghoushchi Saeid , Baradaran Vahid , Mardani Abbas
Published: August 2020

Regions detection has an influence on the better treatment of brain tumors. Existing algorithms in the early detection of tumors are difficult to diagnose reliably. In this paper, we introduced a new robust algorithm using three methods for the classification of brain disease. The first method is Wavelet-Generalized Autoregressive Conditional Heteroscedasticity-K-Nearest Neighbor (W-GARCH-KNN). The Two-Dimensional Discrete Wavelet (2D-DWT) is utilized as the input images. The sub-banded wavelet coefficients are modeled using the GARCH model. The features of the GARCH model are considered as the main property vector. The second method is the Developed Wavelet-GARCH-KNN (D-WGK), which solves the incompatibility of the WGK method for the use of a low pass sub-band. The third method is the Wavelet Local Linear Approximation (LLA)-KNN, which we used for modeling the wavelet sub-bands. The extracted features were applied separately to determine the normal image or brain tumor based on classification methods. The classification was performed for the diagnosis of tumor types. The empirical results showed that the proposed algorithm obtained a high rate of classification and better practices than recently introduced algorithms while requiring a smaller number of classification features. According to the results, the Low-Low sub-bands are not adopted with the GARCH model; therefore, with the use of homomorphic filtering, this limitation is overcome. The results showed that the presented Local Linear (LL) method was better than the GARCH model for modeling wavelet sub-bands.
Financial Distress Prediction and Feature Selection in Multiple Periods by Lassoing Unconstrained Distributed Lag Non-linear Models
Authors: Yan Dawen , Chi Guotai , Lai Kin Keung
Published: August 2020

In this paper, we propose a new framework of a financial early warning system through combining the unconstrained distributed lag model (DLM) and widely used financial distress prediction models such as the logistic model and the support vector machine (SVM) for the purpose of improving the performance of an early warning system for listed companies in China. We introduce simultaneously the 3~5-period-lagged financial ratios and macroeconomic factors in the consecutive time windows t − 3, t − 4 and t − 5 to the prediction models; thus, the influence of the early continued changes within and outside the company on its financial condition is detected. Further, by introducing lasso penalty into the logistic-distributed lag and SVM-distributed lag frameworks, we implement feature selection and exclude the potentially redundant factors, considering that an original long list of accounting ratios is used in the financial distress prediction context. We conduct a series of comparison analyses to test the predicting performance of the models proposed by this study. The results show that our models outperform logistic, SVM, decision tree and neural network (NN) models in a single time window, which implies that the models incorporating indicator data in multiple time windows convey more information in terms of financial distress prediction when compared with the existing singe time window models.
Sensitivity Analysis and Simulation of a Multiserver Queueing System with Mixed Service Time Distribution
Authors: Morozov Evsey , Pagano Michele , Peshkova Irina , Rumyantsev Alexander
Published: August 2020

The motivation of mixing distributions in communication/queueing systems modeling is that some input data (e.g., service time in queueing models) may follow several distinct distributions in a single input flow. In this paper, we study the sensitivity of performance measures on proximity of the service time distributions of a multiserver system model with two-component Pareto mixture distribution of service times. The theoretical results are illustrated by numerical simulation of the M/G/c systems while using the perfect sampling approach.
Dynamic Behaviors of a Single Species Stage Structure Model with Michaelis–Menten-TypeJuvenile Population Harvesting
Authors: Yu Xiangqin , Zhu Zhenliang , Chen Fengde
Published: August 2020

A single species stage structure model with Michaelis–Menten-type juvenile population harvesting is proposed and investigated. The existence and local stability of the model equilibria are studied. It shows that for the model, two cases of bistability may exist. Some conditions for the global asymptotic stability of the boundary equilibrium are derived by constructing some suitable Lyapunov functions. After that, based on the Bendixson–Dulac discriminant, we obtain the sufficient conditions for the global asymptotic stability of the internal equilibrium. Our study shows that nonlinear harvesting can make the dynamics of the system more complex than linear harvesting; for example, the system may admit the bistable stability property. Numeric simulations support our theoretical results.
New Cytotoxic Cerebrosides from the Red Sea Cucumber Holothuria spinifera Supported by In-Silico Studies
Authors: Abdelhameed Reda F. A. , Eltamany Enas E. , Hal Dina M. , Ibrahim Amany K. , AboulMagd Asmaa M. , Al-Warhi Tarfah , Youssif Khayrya A. , Abd El-kader Adel M. , Hassanean Hashim A. , Fayez Shaimaa , Bringmann Gerhard , Ahmed Safwat A. , Abdelmohsen Usama Ramadan
Published: August 2020

Bioactivity-guided fractionation of a methanolic extract of the Red Sea cucumber Holothuria spinifera and LC-HRESIMS-assisted dereplication resulted in the isolation of four compounds, three new cerebrosides, spiniferosides A (1), B (2), and C (3), and cholesterol sulfate (4). The chemical structures of the isolated compounds were established on the basis of their 1D NMR and HRMS spectral data. Metabolic profiling of the H. spinifera extract indicated the presence of diverse secondary metabolites, mostly hydroxy fatty acids, diterpenes, triterpenes, and cerebrosides. The isolated compounds were tested for their in vitro cytotoxicities against the breast adenocarcinoma MCF-7 cell line. Compounds 1, 2, 3, and 4 displayed promising cytotoxic activities against MCF-7 cells, with IC50 values of 13.83, 8.13, 8.27, and 35.56 µM, respectively, compared to that of the standard drug doxorubicin (IC50 8.64 µM). Additionally, docking studies were performed for compounds 1, 2, 3, and 4 to elucidate their binding interactions with the active site of the SET protein, an inhibitor of protein phosphatase 2A (PP2A), which could explain their cytotoxic activity. This study highlights the important role of these metabolites in the defense mechanism of the sea cucumber against fouling organisms and the potential uses of these active molecules in the design of new anticancer agents.
Recent Advances in Astaxanthin Micro/Nanoencapsulation to Improve Its Stability and Functionality as a Food Ingredient
Authors: Martínez-Álvarez Óscar , Calvo Marta M. , Gómez-Estaca Joaquín
Published: August 2020

Astaxanthin is a carotenoid produced by different organisms and microorganisms such as microalgae, bacteria, yeasts, protists, and plants, and it is also accumulated in aquatic animals such as fish and crustaceans. Astaxanthin and astaxanthin-containing lipid extracts obtained from these sources present an intense red color and a remarkable antioxidant activity, providing great potential to be employed as food ingredients with both technological and bioactive functions. However, their use is hindered by: their instability in the presence of high temperatures, acidic pH, oxygen or light; their low water solubility, bioaccessibility and bioavailability; their intense odor/flavor. The present paper reviews recent advances in the micro/nanoencapsulation of astaxanthin and astaxanthin-containing lipid extracts, developed to improve their stability, bioactivity and technological functionality for use as food ingredients. The use of diverse micro/nanoencapsulation techniques using wall materials of a different nature to improve water solubility and dispersibility in foods, masking undesirable odor and flavor, is firstly discussed, followed by a discussion of the importance of the encapsulation to retard astaxanthin release, protecting it from degradation in the gastrointestinal tract. The nanoencapsulation of astaxanthin to improve its bioaccessibility, bioavailability and bioactivity is further reviewed. Finally, the main limitations and future trends on the topic are discussed.
Proteo-Transcriptomic Analysis Identifies Potential Novel Toxins Secreted by the Predatory, Prey-Piercing Ribbon Worm Amphiporus lactifloreus
Authors: von Reumont Björn Marcus , Lüddecke Tim , Timm Thomas , Lochnit Günter , Vilcinskas Andreas , von Döhren Jörn , Nilsson Maria A.
Published: August 2020

Nemerteans (ribbon worms) employ toxins to subdue their prey, but research thus far has focused on the small-molecule components of mucus secretions and few protein toxins have been characterized. We carried out a preliminary proteotranscriptomic analysis of putative toxins produced by the hoplonemertean Amphiporus lactifloreus (Hoplonemertea, Amphiporidae). No variants were found of known nemertean-specific toxin proteins (neurotoxins, cytotoxins, parbolysins or nemertides) but several toxin-like transcripts were discovered, expressed strongly in the proboscis, including putative metalloproteinases and sequences resembling sea anemone actitoxins, crown-of-thorn sea star plancitoxins, and multiple classes of inhibitor cystine knot/knottin family proteins. Some of these products were also directly identified in the mucus proteome, supporting their preliminary identification as secreted toxin components. Two new nemertean-typical toxin candidates could be described and were named U-nemertotoxin-1 and U-nemertotoxin-2. Our findings provide insight into the largely overlooked venom system of nemerteans and support a hypothesis in which the nemertean proboscis evolved in several steps from a flesh-melting organ in scavenging nemerteans to a flesh-melting and toxin-secreting venom apparatus in hunting hoplonemerteans.
Effects of Chitosan Oligosaccharide on Plasma and Hepatic Lipid Metabolism and Liver Histomorphology in Normal Sprague-Dawley Rats
Authors: Liu Shing-Hwa , Chen Rui-Yi , Chiang Meng-Tsan
Published: August 2020

Chitosan oligosaccharide is known to ameliorate hypercholesterolemia and diabetes. However, some studies found that chitosan oligosaccharide might induce mild to moderate hepatic damage in high-fat (HF) diet-induced obese rats or diabetic rats. Chitosan oligosaccharide can be as a dietary supplement, functional food, or drug. Its possible toxic effects to normal subjects need to be clarified. This study is designed to investigate the effects of chitosan oligosaccharide on plasma and hepatic lipid metabolism and liver histomorphology in normal Sprague-Dawley rats. Diets supplemented with 5% chitosan oligosaccharide have been found to induce liver damage in HF diet-fed rats. We therefore selected 5% chitosan oligosaccharide as an experimental object. Rats were divided into: a normal control diet group and a normal control diet +5% chitosan oligosaccharide group. The experimental period was 12 weeks. The results showed that supplementation of 5% chitosan oligosaccharide did not significantly change the body weight, food intake, liver/adipose tissue weights, plasma lipids, hepatic lipids, plasma levels of AST, ALT, and TNF-α/IL-6, hepatic lipid peroxidation and anti-oxidative enzyme activities, fecal lipids, and liver histomorphology in normal rats. These findings suggest that supplementation of 5% chitosan oligosaccharide for 12 weeks may not induce lipid metabolism disorder and liver toxicity in normal rats.
Identification, Purification and Molecular Characterization of Chondrosin, a New Protein with Anti-tumoral Activity from the Marine Sponge Chondrosia Reniformis Nardo 1847
Authors: Scarfì Sonia , Pozzolini Marina , Oliveri Caterina , Mirata Serena , Salis Annalisa , Damonte Gianluca , Fenoglio Daniela , Altosole Tiziana , Ilan Micha , Bertolino Marco , Giovine Marco
Published: August 2020

Chondrosia reniformis is a common marine demosponge showing many peculiarities, lacking silica spicules and with a body entirely formed by a dense collagenous matrix. In this paper, we have described the identification of a new cytotoxic protein (chondrosin) with selective activity against specific tumor cell lines, from C. reniformis, collected from the Liguria Sea. Chondrosin was extracted and purified using a salting out approach and molecular weight size exclusion chromatography. The cytotoxic fractions were then characterized by two-dimensional gel electrophoresis and mass spectrometry analysis and matched the results with C. reniformis transcriptome database. The procedure allowed for identifying a full-length cDNA encoding for a 199-amino acids (aa) polypeptide, with a signal peptide of 21 amino acids. The mature protein has a theoretical molecular weight of 19611.12 and an IP of 5.11. Cell toxicity assays showed a selective action against some tumor cell lines (RAW 264.7 murine leukemia cells in particular). Cell death was determined by extracellular calcium intake, followed by cytoplasmic reactive oxygen species overproduction. The in silico modelling of chondrosin showed a high structural homology with the N-terminal region of the ryanodine receptor/channel and a short identity with defensin. The results are discussed suggesting a possible specific interaction of chondrosin with the Cav 1.3 ion voltage calcium channel expressed on the target cell membranes.
Numerical Simulation of Latent Heat of Solidification for Low Pressure Casting of Aluminum Alloy Wheels
Authors: Zheng Qingchun , Xiao Yinhong , Zhang Tao , Zhu Peihao , Ma Wenpeng , Liu Jingna
Published: August 2020

In this paper, aiming at focusses on many problems existing in the mathematical model of temperature change in the low-pressure casting solidification process of aluminum alloy wheel hub, there is a big gap between the simulation and the actual temperature change, which affects the research on the solidification defects of the wheel hub. In order to study the solidification behavior of aluminum alloy hub in low-pressure casting process, the mathematical model describing the temperature change in the process of casting solidification is established by using different solidification latent heat methods. through finite element simulation and experiment, the temperature change in the process of aluminum alloy (A356) solidification is obtained to compare the difference between the temperature change described by different mathematical models, simulation and experiment. The results show that the temperature numerical model of "the temperature compensation heat capacity method" proposed in this paper is most consistent with the simulation temperature change during the solidification process of the aluminum alloy wheel in the simulation mold, which lays a good theoretical foundation for the study of the low-pressure casting process of the aluminum alloy wheel hub.
In Situ 3D-µ-Tomography on Particle-Reinforced Light Metal Matrix Composite Materials under Creep Conditions
Authors: Camin Bettina , Hansen Lennart
Published: August 2020

In transportation light metal matrix composites (L-MMCs) are used increasingly due to their improved creep resistance even at higher application temperatures. Therefore, the creep behavior and failure mechanisms of creep loaded particle reinforced L-MMCs have been investigated intensively. Until now, creep damage analyses are usually performed ex situ by means of interrupted creep experiments. However, ex situ methods do not provide sufficient information about the evolution of creep damage. Hence, in situ synchrotron X-ray 3D-µ-tomography investigations were carried out enabling time and space resolved studies of the damage mechanisms in particle-reinforced titanium- and aluminum-based metal matrix composites (MMCs) during creep. The 3D-data were visualized and existing models were applied, specifying the phenomenology of the damage in the early and late creep stages. During the early stages of creep, the damage is determined by surface diffusion in the matrix or reinforcement fracture, both evolving proportionally to the macroscopic creep curve. In the late creep stages the damage mechanisms are quite different: In the Al-MMC, the identified mechanisms persist proportional to creep strain. In contrast, in the titanium-MMC, a changeover to the mechanism of dislocation creep evolving super-proportionally to creep strain occurs.
Changes of Multiphase Flow Patterns during Steel Tapping with Simultaneous Argon Bottom Stirring in the Ladle
Authors: Nájera-Bastida Alfonso , Rodríguez-Ávila Jafeth , Guarneros-Guarneros Javier , Morales Rodolfo D. , Chattopadhyay Kinnor
Published: August 2020

Changes of unsteady multiphase fluid flow patterns of liquid steel during electric arc furnace-ladle tapping operations, with simultaneous argon bottom injection, are simulated using interfacial tracking computing techniques. The impinging steel jet interacts with the argon bubbling plume, suffering mutual bending effects, and imparting non-symmetric flows of liquid steel during the whole ladle filling time. At low bath levels, radial recirculating flows are generated and at high bath levels, these flows are substituted by vertical long flows generated by the permanent interaction between the impinging jet and the argon plume. Turbulence intensity increases as the bath level rises. Low bath levels are suitable for pre-melting and preheating ferroalloy particles. High bath levels of steel in the ladle, close to total ladle filling, are the most suitable conditions for thermal and chemical homogenizations. Argon gas forms an intermittent blanket over the air–liquid steel mix due to its higher density than air during the whole ladle filling time.
Setting the Basis for the Interpretation of Temperature First Order Reversal Curve (TFORC) Distributions of Magnetocaloric Materials
Authors: Moreno-Ramírez Luis M. , Franco Victorino
Published: August 2020

First Order Reversal Curve (FORC) distributions of magnetic materials are a well-known tool to extract information about hysteresis sources and magnetic interactions, or to fingerprint them. Recently, a temperature variant of this analysis technique (Temperature-FORC, TFORC) has been used for the analysis of the thermal hysteresis associated with first-order magnetocaloric materials. However, the theory supporting the interpretation of the diagrams is still lacking, limiting TFORC to a fingerprinting technique so far. This work is a first approach to correlate the modeling of first-order phase transitions, using the Bean–Rodbell model combined with a phenomenological transformation mechanism, with the features observed in experimental TFORC distributions of magnetocaloric materials. The different characteristics of the transformations, e.g., transition temperatures, symmetry, temperature range, etc., are correlated to distinct features of the distributions. We show a catalogue of characteristic TFORC distributions for magnetocaloric materials that exhibit some of the features observed experimentally.
Mechanical Anisotropy Induced by Strain Path Change for AZ31 Mg Alloy Sheet
Authors: Yang Chong , Mei Yibing , Meng Dan , Zhu Guoguo , Liu Shengwei , Peng Yan , Wu Lu , Zha Chunyan , Shi Baodong
Published: August 2020

The variation of strain paths induces anisotropy during practical sheet forming processes, which is very important for the subsequent processing technology of anisotropic Mg alloys. In this study, two-step loading tests (tension-tension) were performed to clarify the effect of strain path changes on the evolution of anisotropy on rolled AZ31 sheet. Specimens were preloaded with tension along the rolling direction (RD) with 9% of prestrain. Then, second tension was conducted along 0°, 30°, 45°, 60° and 90° from the RD. It was found that yield strength during the second loading increased along the same direction compared to uniaxial tension without prestraining. For the second loading, the yield strength and flow stress decreased with the increase of the angle from the RD. It was found that the strain path change resulted in stronger anisotropy than that induced by texture. Moreover, it was found that the main deformation modes were basal and prismatic slips during the second loading based on visco-plastic self-consistent (VPSC) modeling. The relative activities of basal and prismatic slips were affected by the second loading direction due to texture evolution. The mechanical anisotropy induced by strain path changes was ascribed to the coupling of the heterogeneous distribution of dislocations and texture evolution induced by prestraining.