bluuebunny/crossref_metadata_2025 huggingface dataset:
Incorporation of Mean/Maximum Stress Effects in the Multiaxial Racetrack Filter
Authors: Meggiolaro Marco Antonio , Tupiassú Pinho de Castro Jaime , Wu Hao
Published: July 2018

This work extends the Multiaxial Racetrack Filter (MRF) to incorporate mean or maximum stress effects, adopting a filter amplitude that depends on the current stress level along the stress or strain path. In this way, a small stress or strain amplitude event can be filtered out if associated with a non-damaging low mean or peak stress level, while another event with the very same amplitude can be preserved if happening under a more damaging high mean or peak stress level. The variable value of the filter amplitude must be calculated in real time, thus it cannot depend on the peak or mean stresses along a load event, because it would require cycle identification and as so information about future events. Instead, mean/maximum stress effects are modeled in the filter as a function of the current (instantaneous) hydrostatic or normal stress along the multiaxial load path, respectively for invariantbased and critical-plane models. The MRF efficiency is evaluated from tension-torsion experiments in 316L stainless steel tubular specimens under non-proportional (NP) load paths, showing it can robustly filter out nondamaging events even under multiaxial NP variable amplitude loading histories. KEYWORDS. Multiaxial racetrack filter; Mean/peak stress effects; Nondamaging events; Multiaxial loads.
The effect of ply folds as manufacturing defect on the fatigue life of CFRP materials
Authors: Hörrmann S. , Adumitroaie A. , Schagerl M.
Published: July 2018

Manufacturing defects are inherent to any manufacturing process. However, in composite materials they might be unavoidable, e.g. ply waviness or even folds of plies are present in complex shaped parts during high pressure resin transfer molding of carbon fiber reinforced polymers. In this work, the effect of the ply folds on the fatigue life of the composite material is investigated. Folds along fiber direction (as they commonly appear during manufacturing) were artificially introduced in unidirectional non crimp fabric plies. The target of this study is the prediction of damage initiation due to this particular type of manufacturing defect. The folds locally increase the fiber volume fraction and also introduce resin rich areas. Fatigue tests in fiber direction and transverse to fiber direction are performed at different load ratios under constant amplitude loading. The influence of the defect geometry on damage initiation and progression is investigated at different scales by non-destructive methods before testing, continuous strain measurement and monitoring the damage progression during testing and fractography analysis after final failure. Most of the time, the first damage was observed at the location of the introduced fold for all considered load cases. However, it was also found, that the folds lead to no significant reduction in fatigue life.
Effect of molding processes on multiaxial fatigue strength in short fibre reinforced polymer
Authors: Sawada Takahiko , Aoyama Hiroshi
Published: July 2018

This study concerns the multiaxial static and fatigue strength properties. Short-glass-fibre-reinforced phenolic-resin composites (SGP) molded by injection and compression processes were subjected to tensiontorsion combined static and fatigue tests at room temperature under various test conditions. Tension – torsion combined static strength well agreed with Tsai-Hill failure criteria without depending on processes. Relationships between the maximum principal stress, ?p1, max, and the number of fracture cycles, Nf, were approximately linear in the whole range of up to 106 cycles. For a unified evaluation of multiaxial fatigue life for SGP, non-dimensional effective stress, ?*, defined by modifying Tsai-Hill failure criteria was applied. The slopes of ?*- Nf curves according to Baskin’s law were almost identical to the injection (n = 26.3) and compression (n = 26.2). We finally confirmed that the multiaxial fatigue life of SFRP could be predicted by using ?* with a unique Wöhler curve without relying on molding processes.
Theorical study on mechanical properties of AZ31B Magnesium alloy Sheets under multiaxial loading
Authors: Znaidi A. , Daghfas O. , Guellouz S. , Nasri R.
Published: July 2018

Numerical simulation by plastic deformation of the shaping processes currently has a large industrial interest. It allows you to shorten the time of design and construction related products and tools to analyze and to optimize processes. An essential part of simulation tools is the constitutive law used to describe the material used. The activity of characterization and modeling of material behavior of the plastic deformation shaping remains a very important research field of activity; the objective of proposing laws of behavior used in computer codes, essentially based on finite element is sufficiently to represent the real behavior of materials. Considering the nature of the materials used and the stresses they experience the behavior laws account for several requirements which make them increasingly complicated. Among these requirements, we cite in particular plastic anisotropy, the great transformations, the complexity and diversity of loads, etc. The complexity of these laws makes them more difficult to implement and in particular to identify: the classic tests are no longer sufficient for identification. The objective of this work is based on two essential points: Suggest a construction strategy, particularly of identifying laws elastoplastic behavior anisotropic operational for the numerical simulation of plastic deformation shaping processes with particular attention to sheet metal magnesium. Magnesium sheet metal manufacturing process involves rolling operation. In a cost-cutting goal, this operation now takes place cold, implying a very marked anisotropy of the material at the output of the mill.
Ductile fracture modelling and J-Q fracture mechanics: a constraint based fracture assessment approach
Authors: Larrosa N.O. , Ainsworth R.A.
Published: July 2018

The reduced state of stress triaxiality observed in shallow cracked components allows an increased capacity to resist crack propagation compared to that observed in deeply cracked specimens. This may be regarded as a higher fracture toughness value which allows a reduction in the inherent conservatism when assessing components in low constraint conditions. This study uses a two-parameter fracture mechanics approach (JQ) to quantify the level of constraint in a component (e.g. a pipe with a surface crack) and in fracture test specimens, i.e. single edge tension [SE(T]) and compact tension [C(T)] specimens, of varying constraint level. The level of constraint of the component is matched to a specific test specimen and therefore the ability of the structure to resist fracture is given by the fracture toughness of the test specimen with a similar J-Q response. Fracture toughness values for different specimens have been obtained from tearing resistance curves (J-R curves) constructed by means of a virtual testing framework. The proposed engineering approach shows that the combination of a local approach and two-parameter fracture mechanics can be used as a platform to perform more accurate fracture assessments of defects in structures with reduced constraint conditions.
Pressure vessels design methods using the codes, fracture mechanics and multiaxial fatigue
Authors: Majid Fatima , Nattaj Jilali , Elghorba Mohamed
Published: July 2018

This paper gives a highlight about pressure vessel (PV) methods of design to initiate new engineers and new researchers to understand the basics and to have a summary about the knowhow of PV design. This understanding will contribute to enhance their knowledge in the selection of the appropriate method. There are several types of tanks distinguished by the operating pressure, temperature and the safety system to predict. The selection of one or the other of these tanks depends on environmental regulations, the geographic location and the used materials. The design theory of PVs is very detailed in various codes and standards API, such as ASME, CODAP ... as well as the standards of material selection such as EN 10025 or EN 10028. While designing a PV, we must design the fatigue of its material through the different methods and theories, we can find in the literature, and specific codes. In this work, a focus on the fatigue lifetime calculation through fracture mechanics theory and the different methods found in the ASME VIII DIV 2, the API 579-1 and EN 13445-3, Annex B, will be detailed by giving a comparison between these methods. In many articles in the literature the uniaxial fatigue has been very detailed. Meanwhile, the multiaxial effect has not been considered as it must be. In this paper we will lead a discussion about the biaxial fatigue due to cyclic pressure in thick-walled PV. Besides, an overview of multiaxial fatigue in PVs is detailed. KEYWORDS. Pressure vessel design; ASME VIII; Multiaxial fatigue; Fracture mechanics; Cumulative damage
Structural mechanisms of formation of adiabatic shear bands
Authors: Sokovikov Mikhail , Bilalov Dmitry , Oborin Vladimir , Chudinov Vasiliy , Uvarov Sergey , Bayandin Yuriy , Naimark Oleg
Published: July 2018

The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the size of grains is ~300nm. Rotational deformation modes give rise to the high angular disorientations of grains. The development of plastic shear instability regions has been simulated numerically. For this purpose, we use a recently developed theory, in which the influence of microshears on the deformation properties of materials has been studied by the methods of statistical physics and thermodynamics of irreversible processes. The results of theoretical and experimental studies suggest that one of the mechanisms of the plastic shear instability and localization of plastic strain at high-velocity perforation is related to structural and kinetic transitions in microshear ensembles.
The effect of varying loading directions and loading levels on crack growth at 2D- and 3D-mixed-mode-loadings
Authors: Eberlein A. , Richard H.A.
Published: July 2018

While product’s operation the loading situation commonly changes. The local loading situation on an existing crack then can shift to a combined loading, composed of mode I, mode II and mode III, and consequently influence the product’s durability significantly. This influence on further fatigue crack growth and structures’ failure can be positive or negative. Present article describes and discusses the effect of varying loading directions from mode I- to 2D-mixed-mode-loading as well as from mode I- to mixedmode I + III-loading. Moreover, experiments on varying loading levels are performed by interspersing mixed-mode block loads in cyclic mode I base load, cyclic mode II base load as well as in cyclic mode III base load.
Probabilistic prediction of fatigue damage based on linear fracture mechanics
Authors: Krejsa M. , Koubova L. , Flodr J. , Protivinsky J. , Nguyen Q. T.
Published: July 2018

Paper describes in detail and gives example of the probabilistic assessment of a steel structural element subject to fatigue load, particular attention being paid to cracks from the edge and those from surface. Fatigue crack damage depends on a number of stress range cycles. Three sizes are important for the characteristics of the propagation of fatigue cracks - the initial size, detectable size and acceptable size. The theoretical model of fatigue crack progression in paper is based on a linear fracture mechanics. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability, times for subsequent inspections can be determined. For probabilistic calculation of fatigue crack progression was used the original and new probabilistic methods - the Direct Optimized Probabilistic Calculation (“DOProC”), which is based on optimized numerical integration. The algorithm of the probabilistic calculation was applied in the FCProbCalc code (“Fatigue Crack Probabilistic Calculation”), using which is possible to carry out the probabilistic modelling of propagation of fatigue cracks in a user friendly environment very effectively.
3D Stress intensity factor and T-stresses (T11 and T33) formulations for a Compact Tension specimen
Authors: Kudari S. K. , Kodancha K. G.
Published: July 2018

The paper describes test specimen thickness effect on stress intensity factor (KI), and T-stresses stresses (T11 and T33) for a Compact Tension specimen. Formulations to estimate 3D KI, T11 and T33 stresses are proposed based on extensive 3D Finite element analyses. These formulations help to estimate magnitudes of 3D KI and T11 and T33 which are helpful to quantify in-plane and out-of- plane constraint effect of the crack tip. The proposed formulations are validated with the similar results available in literature and found to be within acceptable error.
Experimental investigation on fracture toughness of Al6061–graphite by using Circumferential Notched Tensile Specimens
Authors: Doddamani Saleemsab , Kaleemulla Mohamed
Published: July 2018

This paper presents the experimental work carried out on the fracture behavior of aluminium 6061 (Al6061) and graphite particulate composites. The required specimens are prepared using stir casting method with graphite proportions ranging from 3 to 12 % by weight. The fracture behavior of Al6061-graphite particulate composites produced using stir casting method, was investigated by conducting experiments on Universal Testing Machine (UTM). Circumferential Notched Tensile (CNT) specimens were utilized to evaluate the fracture toughness of the composites. From the experiment the fracture toughness KIC= 15.85MPa m1/2 is obtained for Al6061-9% Graphite. Further, the experimental results revealed that, except 12% graphite, the fracture toughness of Al6061-graphite was observed to increases with an increase in weight percentage of graphite. The experimental results reinforce that Al6061-graphite particulate MMCs are suitable for automotive and aerospace applications requiring high fracture toughness apart from good wear resistance.
Correlation between the electric and acoustic signals emitted during compression of brittle materials
Authors: Pasiou Ermioni D. , Triantis Dimos
Published: July 2018

An experimental protocol is described including a series of uniaxial compression tests of three brittle materials (marble, mortar and glass). The Acoustic Emission (AE) technique and the Pressure Stimulated Currents (PSC) one are used since the recordings of both techniques are strongly related to the formation of cracking in brittle materials. In the present paper, the correlation of these techniques is investigated, which is finally proven to be very satisfactory.
The multi-layered ring under parabolic distribution of radial stresses combined with uniform internal and external pressure
Authors: Markides Christos F. , Pasiou Ermioni D. , Kourkoulis Stavros K.
Published: July 2018

A recently introduced solution for the stress- and displacementfields, developed in a multi-layered circular ring, composed of a finite number of linearly elastic concentric layers, subjected to a parabolic distribution of radial stresses, is here extended to encompass a more general loading scheme, closer to actual conditions. The loading scheme includes, besides the parabolic radial stresses, a combination of uniform pressures acting along the outer- and innermost boundaries of the layered ring. The analytic solution of the problem is achieved by adopting Savin’s pioneering approach for an infinite plate with a hole strengthened by rings. Taking advantage of the results provided by the analytic solution, a numerical model, simulating the configuration of a threelayered ring (quite commonly encountered in practical applications) is validated. The numerical model is then used for a parametric analysis enlightening some crucial aspects of the overall response of the ring.
Notched multiaxial fatigue of Al7050-T7451: on the need for an equivalent process zone size
Authors: Sá M.V.C , Ferreira J.L.A , da Silva C.R.M , Araújo J.A.
Published: July 2018

The aim of this work is to investigate stress gradient effects on the fatigue life estimation of notched Al 7050-T7451 specimens under combined torsion and push-pull loading conditions. Initially, simple push-pull and torsion fatigue tests in plain and notched specimens were independently conducted not only to obtain the material properties necessary to calibrate a standard multiaxial critical plane based model, but also to raise the critical distance versus life curves in tension (L? – Nf) and in torsion (L? – Nf). This latter step also required a Finite Element Elastic Stress Analysis of the notched specimens tested in the medium high-cycle fatigue regime. Then, proportional multiaxial fatigue tests were carried out using this same notched geometry. The combination of a multiaxial model with the theory of critical distance (TCD) was applied to estimate fatigue lives. For this aluminium alloy, neither the use of the L? – Nf nor L? – Nf combined with the predictive multiaxial model was able to estimate lives in an accurate way.
Experimental evaluation of CTOD in constant amplitude fatigue crack growth from crack tip displacement fields
Authors: Vasco-Olmo J.M. , Diaz F.A. , Antunes F.V. , James M.N.
Published: July 2018

In the current work an experimental study of the crack tip opening displacement (CTOD) is performed to evaluate the ability of this parameter to characterise fatigue crack growth. A methodology is developed to measure and to analyse the CTOD from experimental data. The vertical displacements measured by implementing Digital Image Correlation on growing fatigue cracks are used to measure the CTOD. Fatigue tests at R ratios of 0.1 and 0.6 were conducted on compact-tension specimens manufactured from commercially pure titanium. A sensitivity analysis was performed to explore the effect of the position selected behind the crack tip for the CTOD measurement. The analysis of a full loading cycle allowed identifying the elastic and plastic components of the CTOD. The plastic CTOD was found to be directly related to the plastic deformation at the crack tip. Moreover, a linear relationship between da/dN and the plastic CTOD for both tests was observed. Results show that the CTOD can be used as a viable alternative to ?K in characterising fatigue crack propagation because the parameter considers fatigue threshold and crack shielding in an intrinsic way. This work is intended to contribute to a better understanding of the different mechanisms driving fatigue crack growth and the address the outstanding controversy associated with plasticity-induced fatigue crack closure.
Gradient approach for the evaluation of the fatigue limit of welded structures under complex loading
Authors: Nadot Y. , Halm D. , Dal Cero Coelho F.
Published: July 2018

Welded ‘T-junctions’ are tested at different load ratio for constant and variable amplitude loading. Fatigue results are analyzed through the type of fatigue mechanisms depending on the loading type. A gradient approach (WSG: Welded Stress Gradient) is used to evaluate the fatigue limit and the comparison with experimental results shows a relative good agreement. Nonlinear cumulative damage theory is used to take into account the variable amplitude loading.
Review of the Influence of non-singular higher order terms on the stress field of thin welded lap joints and small inclined cracks in plates
Authors: Berto F. , Ayatollahi M.R. , Vantadori S. , Carpinteri A.
Published: July 2018

In stress analysis of cracked plates, alongside the stress intensity factor which quantifies the singular stress component perpendicular to the crack plane, the role played in crack growth by the constant term parallel to the crack plane, called the T-stress, has been widely investigated by many researchers. There are, however, cases of practical interest where the influence on the stress field of the higher order terms in the series expansion for the crack tip stress field, is not negligible. The main aim of the present investigation is to present and apply a set of equations able to describe more accurately the stress components for those cases where the mode I and mode II stress intensity factors used in combination with the T-stress are unable to characterise with sufficient precision the complete stress field ahead the crack tip. The starting point is represented by the Williams’ solution (Williams, 1957) where stresses as expressed in terms of a power series. An example is investigated of a thin-thickness welded lap joint characterized by various joint width to thickness ratios, in the range of d/t ranging from 0.5 to 5. The present paper indicates that the local stresses as well as the strain energy averaged over a control volume which embraces the slip tip, can be evaluated with satisfactory precision only by taking into account a further four terms besides KI, KII and T-stress.
Study on the effect of new type liquid accelerator on the performance of shotcrete
Authors: Zhang Luchen , Li Shuchen , Yan Qin , Zhu Lin
Published: July 2018

Shotcrete is an essential preliminary support means in New Austrian Tunneling Method (NATM) construction and plays a very important role in controlling the stability of surrounding rock. The accelerator is a necessary admixture in shotcrete and its quality can greatly affect shotcrete performance. This paper proposes a new liquid accelerator characterized by short initial and final setting time, small dosage, and good adaptability to cement. Laboratory tests and field tests are conducted to verify the influence of this liquid accelerator on performance of shotcrete. Numerical simulation is carried out to study the strength growth of shotcrete with time and interaction between the strength and stress release of surrounding rock. The results show that the initial and final setting time of this liquid accelerator is 2 minutes and 4 minutes respectively. Its dosage is just 1.5% to 4% of the cement quantity. Adding this liquid accelerator can effectively improve the early strength and reduce the later strength loss of shotcrete, and therefore enhance the supporting effects of shotcrete on surrounding rock. In the field application, it is an ideal liquid accelerator for shotcrete, characterized by little resilience, no slurry shedding, and low dust.
Carbon nano-tubes in improving the mechanical property of cement-based composite materials
Authors: Wu Xu , Dai Li
Published: July 2018

Carbon nano-tubes as a kind of novel nanometer material have been extensively applied in cement-based composite materials to improve their properties. This study prepared carbon nano-tubes cement based composite materials by evenly scattering carbon nano-tubes in cement materials using ultrasonic method and emphatically investigation the improvement of the mechanical property. The results demonstrated that, the addition of carbon nano-tubes could significantly relieve the mechanical properties of cement based composite materials. When the mixing amount of carbon nano-tubes reached the optimal value, i.e., 0.1%, the improvement of the mechanical property of the carbon nano-tubes cement based composite materials was the best. The microstructure analysis using scanning electron microscope suggested that, carbon nano-tubes produced bridging and pullout effects in the cement-based materials, which enhanced the damage resistance of the cement based materials.
Fracture assessment of magnetostrictive materials
Authors: Peron M. , Razavi S.M.J. , Berto F. , Torgersen J. , Colussi M.
Published: July 2018

Giant magnetostrictive materials are gaining interest in the field of smart material, especially the commercially known Terfenol-D, that is an alloy made out of iron, terbium and dysprosium (Tb0.3Dy0.7Fe1.9). Since these smart materials are subjected to both mechanical loads and magnetic field during their industrial applications, an extensive characterization on the influence of a magnetic field and of defects on their fracture behavior is needed. Very few works can be found in literature about this topic and, thus, the purpose of this work is to partially fill this lack by means of three-point bending tests on single-edge pre-cracked Terfenol-D specimens. Failure loads have been measured at different loading rates and under magnetic fields of various intensities. Since giant magnetostrictive materials are very brittle, the strain energy density (SED) approach has been exploited by means of couplefield finite element analyses. SED has revealed itself as a robust parameters in the assessment of the magnetic field and loading rate effects on fracture resistance, allowing also to propose a relationship between the radius of the control volume and the loading-rate.
The Behaviour and Productivity of Mid-Lactation Dairy Cows Provided Daily Pasture Allowance over 2 or 7 Intensively Grazed Strips
Authors: Verdon Megan , Rawnsley Richard , Raedts Pieter , Freeman Mark
Published: July 2018

Research into the effects of intense grazing regimes on cattle behaviour and productivity will support the ethical intensification of pastoral dairy production. Two treatments were applied to two herds of 30 mid-lactation cows over 28 days. Cows were offered an estimated 12 kg DM/cow (above 5 cm from ground level) of irrigated pasture per day. The control herd received their daily pasture allocation in two equal grazings while the experimental herd received theirs over seven smaller grazings. Backgrazing beyond the current allocation (morning or afternoon) was prevented. Individual records were taken daily for milk production and behaviour (MooMonitor+). Milk composition, energy corrected milk (ECM), and live weight were recorded weekly. Feeding mid-lactation dairy cows over seven smaller grazing allocations reduced the time cows spent ruminating (p < 0.001), milk yield (p < 0.001), and ECM (p < 0.05). However, milk composition, live weight, time feeding, and pasture consumption were not affected by feeding frequency (p > 0.05). Cattle may have adapted their ingestive behaviour in response to the more intensive strip-grazing regime utilised in this study, with negative consequences for digestive processes and consequently milk production. Intense grazing regimes need to support the ingestive, digestive, and social behaviours of cattle.
Chemical Injections Realized with Null Pressure for Underpinning the Foundation of an 18th Century Building Located in the Historical City of Cuenca (Spain)
Authors: Sánchez Lavín José Ramón , Escolano Sánchez Félix , Mazariegos de la Serna Alberto
Published: July 2018

Chemical injection of expansive polyurethane resin in the ground is a well-known technology that is also used for underpinning shallow foundations. It is noteworthy that it has been recently used with success on buildings of great historic value that are part of the country’s architectural heritage. This article describes the work undertaken on a historic building located in the city of Cuenca (Spain), for improving ground condition through injecting below foundation, in order to stop the differential settlements detected in the structure. This technology has proven to be, at least, as effective as the more conventional methods used in the past as supporting the foundation by concrete shafts or micropiles.
Research Progress of Gas Sensor Based on Graphene and Its Derivatives: A Review
Authors: Tian Wenchao , Liu Xiaohan , Yu Wenbo
Published: July 2018

Gas sensors are devices that convert a gas volume fraction into electrical signals, and they are widely used in many fields such as environmental monitoring. Graphene is a new type of two-dimensional crystal material that has many excellent properties including large specific surface area, high conductivity, and high Young’s modulus. These features make it ideally suitable for application for gas sensors. In this paper, the main characteristics of gas sensor are firstly introduced, followed by the preparation methods and properties of graphene. In addition, the development process and the state of graphene gas sensors are introduced emphatically in terms of structure and performance of the sensor. The emergence of new candidates including graphene, polymer and metal/metal oxide composite enhances the performance of gas detection significantly. Finally, the clear direction of graphene gas sensors for the future is provided according to the latest research results and trends. It provides direction and ideas for future research.
Evaluating the Effects of Steel Fibers on Mechanical Properties of Ultra-High Performance Concrete Using Artificial Neural Networks
Authors: Qu Dechao , Cai Xiaoping , Chang Wei
Published: July 2018

Steel fibers enhance the flexural strength, the compressive strength and the ductility of untra-high performance concrete, predicting the flexural strength and the compressive strength of ultra-high performance steel fiber reinforced concrete (UHPFRC) accurately has significant influence on controlling steel fiber volume fraction and optimizing UHPFRC mix proportion. In this study, to evaluate the effects of steel fibers on the mechanical properties of UHPFRC, two artificial neural networks were developed in order to predict the flexural strength and the compressive strength of UHPFRC, respectively. 102 test data sets and 162 test data sets from literature were trained and tested to establish the flexural strength model and the compressive strength model, respectively. In these two models, the influential parameters, including the water to binder ratio, the diameter, the length, the aspect ratio, and the volume fraction of steel fibers, as well as the compressive strength and the flexural strength of concrete without fibers were investigated as the inputs, while the compressive strength and the flexural strength of UHPFRC were the outputs. The results show that the artificial neural network models predicted the compressive strength and flexural strength of UHPFRC accurately. Then, by comparing with existing analytical models, it was determined that the proposed models had high applicability and reliability with respect to predicting the compressive strength and the flexural strength of UHPFRC.
Interaction of Ultrashort Laser Pulses with Atoms in Plasmas
Authors: Astapenko V. A. , Lisitsa V. S.
Published: July 2018

The paper is devoted to the investigation of the absorption of ultrashort laser pulses on atoms in plasmas, accounting for the different broadening mechanisms of atomic resonant transitions. The analysis is made in terms of the absorption probability during the entire interaction between the laser pulse and atom. Attention is mainly given to dependence of probability upon the pulse duration and the carrier frequency of the pulse. The results are presented via dimensionless parameters and functions describing the effect of finite pulse duration on atomic spectra for different broadening mechanisms, namely Doppler, Voigt, Holtsmark and their combinations, as well as the Stark line broadening of Rydberg atomic lines.
Preparation of Yttria-Stabilized Zirconia Hollow Sphere with Reduced Shell Thickness by Controlling Ambient Temperature during Plasma Process
Authors: Zhao Lina , Zhang Zhi , Duan Yugang , Cui Hong , Gao Yong
Published: July 2018

Yttria-stabilized zirconia (YSZ) hollow sphere (HS) powder is a novel potential feedstock material for the plasma spraying of next generation advanced thermal barrier coatings with low thermal conductivity and high sintering resistibility. In this study, YSZ HS powders were prepared by plasma treatment with/without a heat preservation zone around the flying path of the particles during plasma flame. The results of the scanning electron microscopy of YSZ HS powders showed that HS prepared with a heat preservation zone during the plasma process exhibited a regular spherical morphology and a homogeneous thin shell structure. Due to the sufficient heating of the shell regions, the HS powder presented a well densified shell structure. Furthermore, the mechanism of formation of the HS powder with reduced shell thickness was also discussed based on the analysis of the evolution of the powder structure. This kind of hollow sphere powder with a very thin shell structure provides a new alternative feedstock material for the development of next generation high performance thermal barrier coatings.
Corrosion Potential Modulation on Lead Anodes Using Water Oxidation Catalyst Coatings
Authors: Kotyk Juliet , Chen Chi , Sheehan Stafford
Published: July 2018

The oxidation of water to form oxygen gas provides charge balance for the cathodic deposition of metals, such as zinc, in the electrorefining industry. This is a corrosive, four-electron electrochemical reaction that causes deterioration of lead-silver alloy anodes employed in these processes. A sacrificial manganese oxide layer on the anode surface, formed in-situ from manganese sulfate, is used in industry to reduce the corrosion rate of these anodes by preferentially enabling water oxidation rather than lead dissolution. Still, it is poorly understood how the activity of manganese oxide as a water oxidation catalyst relates to its anticorrosive properties. Here, we show how the presence of water oxidation catalysts both formed in-situ (including the industry standard manganese oxide) and heterogenized prior to electrolysis on lead anodes affect the corrosion potential of these anodes. We find that corrosion potential under dynamic polarization conditions is the parameter most affected by the coatings formed in-situ and applied ex-situ prior to electrolysis.
Synergies and Trade-Offs in the Production of NWFPs Predicted in Boreal Forests
Authors: Kurttila Mikko , Pukkala Timo , Miina Jari
Published: July 2018

The global growth of the consumption of non-wood forest products (NWFPs) is evident due to the current trends in lifestyle and consumption. Alongside the increased popularity and commercial use of NWFPs, their yields are also more often taken into account in forest management planning. Empirical yield models recently developed for different NWFPs enable forest managers to include their predicted yields in multi-objective optimization. However, knowledge on the synergies and trade-offs between timber production and different NWFPs is scanty. In this study, we analyzed these relationships through correlation matrices and production possibility frontiers in two case study forest holdings from Finland. A large number of Pareto optimal forest holding level plans were produced by multi-objective optimization and used to analyze trade-offs and synergies. Empirical yield models for 12 NWFPs, representing different berries, mushrooms, and tree-based products, were utilized in the analyses. The results revealed synergies and possibilities for joint-production for NWFPs, but also trade-offs between NWFPs and timber production. NWFPs often had a negative correlation with cutting removals, with the only exception being cowberry. Despite the overall negative correlation, the maximum yields of NWFPs called for some cuttings. Negative correlations with the net present value of timber production were weaker. The results are valuable when the aim is to diversify the use of boreal forests and open avenues for truly multi-objective decision support services to facilitate the decision making of forest owners.
On the Stability of Couples
Authors: Hiller Tobias
Published: July 2018

In this article, we analyze the stability of couples on the marriage market. Recent developments in cooperative game theory allow a new model that uses team games which make it possible to model the marriage market. Coalition structures can model couples. We analyze two cases: a symmetrical one with only one type of men and one type of women; and one with several types of women and men.
Encapsulation of Biological Agents in Hydrogels for Therapeutic Applications
Authors: Pérez-Luna Víctor H. , González-Reynoso Orfil
Published: July 2018

Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This makes them attractive not only for controlled drug delivery of proteins, but they can also be used to encapsulate cells that can have therapeutic applications. Thus, hydrogels can be used to create systems that will deliver required therapies in a controlled manner by either encapsulation of proteins or even cells that produce molecules that will be released from these systems. Here, an overview of hydrogel encapsulation strategies of biological elements ranging from molecules to cells is discussed, with special emphasis on therapeutic applications.
Application of Gold Nanoparticle to Plasmonic Biosensors
Authors: Lee Jin-Ho , Cho Hyeon-Yeol , Choi Hye Kyu , Lee Ji-Young , Choi Jeong-Woo
Published: July 2018

Gold nanoparticles (GNPs) have been widely utilized to develop various biosensors for molecular diagnosis, as they can be easily functionalized and exhibit unique optical properties explained by plasmonic effects. These unique optical properties of GNPs allow the expression of an intense color under light that can be tuned by altering their size, shape, composition, and coupling with other plasmonic nanoparticles. Additionally, they can also enhance other optical signals, such as fluorescence and Raman scattering, making them suitable for biosensor development. In this review, we provide a detailed discussion of the currently developed biosensors based on the aforementioned unique optical features of GNPs. Mainly, we focus on four different plasmonic biosensing methods, including localized surface plasmon resonance (LSPR), surface-enhanced Raman spectroscopy (SERS), fluorescence enhancement, and quenching caused by plasmon and colorimetry changes based on the coupling of GNPs. We believe that the topics discussed here are useful and able to provide a guideline in the development of novel GNP-based biosensors in the future.
The Nitrogen Heterocycle Content of Meteorites and Their Significance for the Origin of Life
Authors: Martins Zita
Published: July 2018

Carbonaceous chondrites are very primitive meteorites that are rich in carbon. They contain many soluble organic compounds, including nitrogen heterocycles. These play a crucial role in present-day living organisms as they are components of the genetic material and of the co-factors of enzymes. This review outlines the nitrogen heterocycle content of carbonaceous meteorites. The potential mechanisms of formation of these molecules are also described. Measurements of the compound-specific carbon and hydrogen isotopic compositions are mentioned as a way of establishing the origin of the nitrogen heterocycles detected in meteorites.
Metagenomic Analysis of Microbial Community Compositions and Cold-Responsive Stress Genes in Selected Antarctic Lacustrine and Soil Ecosystems
Authors: Koo Hyunmin , Hakim Joseph , Morrow Casey , Crowley Michael , Andersen Dale , Bej Asim
Published: July 2018

This study describes microbial community compositions, and various cold-responsive stress genes, encompassing cold-induced proteins (CIPs) and cold-associated general stress-responsive proteins (CASPs) in selected Antarctic lake water, sediment, and soil metagenomes. Overall, Proteobacteria and Bacteroidetes were the major taxa in all metagenomes. Prochlorococcus and Thiomicrospira were highly abundant in waters, while Myxococcus, Anaeromyxobacter, Haliangium, and Gloeobacter were dominant in the soil and lake sediment metagenomes. Among CIPs, genes necessary for DNA replication, translation initiation, and transcription termination were highly abundant in all metagenomes. However, genes for fatty acid desaturase (FAD) and trehalose synthase (TS) were common in the soil and lake sediment metagenomes. Interestingly, the Lake Untersee water and sediment metagenome samples contained histone-like nucleoid structuring protein (H-NS) and all genes for CIPs. As for the CASPs, high abundances of a wide range of genes for cryo- and osmo-protectants (glutamate, glycine, choline, and betaine) were identified in all metagenomes. However, genes for exopolysaccharide biosynthesis were dominant in Lake Untersee water, sediment, and other soil metagenomes. The results from this study indicate that although diverse microbial communities are present in various metagenomes, they share common cold-responsive stress genes necessary for their survival and sustenance in the extreme Antarctic conditions.
Idiopathic ventricular tachycardia in children: curative therapy with radiofrequency ablation
Authors: Bakšienė Dalia , Šileikienė Rima , Šileikis Vytautas , Kazakevičius Tomas , Zabiela Vytautas , Žėbienė Migla , Puodžiukynas Aras
Published: July 2018

Idiopathic ventricular tachycardia is a rare condition, and there is a lack of clear guidelines for the necessity and indications for prophylactic antiarrhythmic or curative treatment. The aim of this study was to review the clinical picture of idiopathic ventricular tachycardia and evaluate the efficacy and safety of radiofrequency ablation therapy in children. Material and methods. The subjects of this study were 16 children with idiopathic ventricular tachycardia. The mean age at onset of idiopathic ventricular tachycardia was 12 years. All patients underwent electrophysiological examination. Nonfluoroscopic mapping technology (CartoTM) was used in one case. Radiofrequency ablation was performed in all children (mean duration of follow-up was 46 months). Results. Six children with idiopathic ventricular tachycardia were free of symptoms. Palpitation was the only complain in four patients, and six patients presented with symptoms of circulatory disorder (the tendency of the higher rate of ventricular tachycardia and more premature contractions and episodes of ventricular tachycardia in one day were noticed in five of them). All children after radiofrequency ablation were alive, and only one complication (complete right bundle branch block) occurred. Success at last follow-up included five children with left and six with right idiopathic ventricular tachycardia. Conclusions. Catheter ablation seems a promising therapeutic option with the outlook possible of the idiopathic ventricular tachycardia in children. It is safe enough and should be considered as the therapy of choice even in children without of symptoms if they wish to live active social and physical life.
Reconfigurable Sensor Analog Front-End Using Low-Noise Chopper-Stabilized Delta-Sigma Capacitance-to-Digital Converter
Authors: Kim Hyungseup , Lee Byeoncheol , Mun Yeongjin , Kim Jaesung , Han Kwonsang , Roh Youngtaek , Song Dongkyu , Huh Seounghoon , Ko Hyoungho
Published: July 2018

This paper proposes a reconfigurable sensor analog front-end using low-noise chopper-stabilized delta-sigma capacitance-to-digital converter (CDC) for capacitive microsensors. The proposed reconfigurable sensor analog front-end can drive both capacitive microsensors and voltage signals by direct conversion without a front-end amplifier. The reconfigurable scheme of the front-end can be implemented in various multi-mode applications, where it is equipped with a fully integrated temperature sensor. A chopper stabilization technique is implemented here to achieve a low-noise characteristic by reducing unexpected low-frequency noises such as offsets and flicker noise. The prototype chip of the proposed sensor analog front-end is fabricated by a standard 0.18-μm 1-poly-6-metal (1P6M) complementary metal-oxide-semiconductor (CMOS) process. It occupies a total active area of 5.37 mm2 and achieves an effective resolution of 16.3-bit. The total power consumption is 0.843 mW with a 1.8 V power supply.
Influence of Extraction Conditions on Ultrasound-Assisted Recovery of Bioactive Phenolics from Blueberry Pomace and Their Antioxidant Activity
Authors: Bamba Bio Sigui Bruno , Shi John , Tranchant Carole C. , Xue Sophia Jun , Forney Charles F. , Lim Loong-Tak
Published: July 2018

The increase in diet-related chronic diseases has prompted the search for health-promoting compounds and methods to ensure their quality. Blueberry pomace is a rich yet underutilized source of bioactive polyphenols. For these high-value bioactive molecules, ultrasound-assisted extraction (USAE) is an attractive and green alternative to conventional extraction techniques for improving purity and yields. This study aimed to assess the impact of USAE parameters (sonication time, solvent composition, solid/liquid ratio, pH and temperature) on the recovery of phenolic compounds from blueberry pomace and antioxidant activity of the extracts. Total phenolic, flavonoid and anthocyanin contents (TPC, TFC and TAC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity were analysed. USAE in 50% ethanol/water was the most efficient, yielding the highest TPC (22.33 mg/g dry matter (DM)), TFC (19.41 mg/g DM), TAC (31.32 mg/g DM) and DPPH radical scavenging activity (41.79 mg Trolox/g DM). USAE in water showed the lowest values even at low (1/40) solid/liquid ratio (7.85 mg/g DM, 3.49 mg/g DM, and 18.96 mg/g DM for TPC, TFC and TAC, respectively). Decreasing the solid/liquid ratio in water or 50% ethanol significantly increased TPC, TFC, TAC and DPPH radical scavenging. With ethanol, increasing the temperature in the range 20–40 °C decreased TPC but increased TFC and DPPH radical scavenging activity. Anthocyanin profiles of water and ethanolic extracts were qualitatively similar, consisting of malvidin, delphinidin, petunidin and cyanidin. These findings indicate that USAE is a method of choice for extracting high-value bioactive phenolics from blueberry pomace. Selective enrichment of different phenolic fractions is possible under select extraction conditions.