bluuebunny/crossref_metadata_2025 huggingface dataset:
Cosmological particle creation beyond de Sitter
Authors: Modak Sujoy K.
Published: February 2019

Over the years, de Sitter spacetime has been a central focus in studies involving quantum fields, for its importance in the early and late expansion stages of the universe. While de Sitter spacetime closely mimics characteristics of the inflationary and dark energy dominated universe, it does not help to understand the radiation and matter dominated expansions. In this paper, we revisit some recent works involving the author which study gravitational particle creation beyond the de Sitter stage. Specifically, we present novel aspects of particle creation in the radiation dominated universe and then provide an analysis of time evolution of the primordial (Bunch–Davies) vacuum state, its particle excitation and quantum versus classical behavior of field modes in a multi-stage universe, comprising of (i) the inflationary de Sitter (ii) the radiation dominated and (iii) the late dark energy dominated stages.
INFLUENCE OF MOLYBDENUM DISULFIDE PARTICLE SIZE ON FRICTION AND WEAR CHARACTERISTICS OF NON-ASBESTOS-BASED COPPER-FREE BRAKE FRICTION COMPOSITES
Authors: VIJAY R. , LENIN SINGARAVELU D. , FILIP PETER
Published: February 2019

Molybdenum disulfide is a successful solid lubricant because of its cleavage of the basal plane at the time of sliding, which helps to retain the lubrication nature in order to reduce wear and to maintain frictional stability. Thus the present study deals with the development of copper-free brake pads using molybdenum disulfide that possesses different grades based on the particle size, namely, technical (coarse), fine and superfine. The brake pads were developed using conventional manufacturing processes and characterized for its physical, chemical, thermal and mechanical properties as per industrial standards. Thermal stability was measured for the varying ingredients and the developed composites using thermogravimetric analyzer instrument. The tribological studies were done using Chase testing following IS2742 Part-4 standards. The results showed that coarse-sized (technical grade) molybdenum disulfide-based brake pads possess better thermal stability with good fade and recovery characteristics in turn leading to less wear when compared with the other two composites. This is because of its better heat dissipation and superior lubricating nature. Scanning electron microscopy and energy dispersive analysis were helpful in studying the wear behavior of the Chase-tested brake friction composite samples.
Solving Post-Buckling Characteristic of Thermal-Resistance Films Attached to Glass Façade via an Optimization Method
Authors: Wu Zhengtian , Zhang Yang , Huan Zhijie
Published: February 2019

A novel thermal-resistance film is proposed, and its thermal post-buckling behavior is studied by using the meshless method. The Von Kármán plate model together with the nonlocal theory is adopted for the formulation of the problem. The post-buckling curve of the graphene sheet (GS) film is obtained. The effect of the parameters, such as nonlocal parameters, geometric size, geometric shape and elastic medium, on the thermal post-buckling response of the GSs film is examined. It is found that it is important to design proper geometric size and geometric shape and control the radius of tensionless area. This study provides theoretical guidance for fire resistance design of thermal-resistance films attached to glass façade.
w = 1/3 to w = −1 evolution in a Robertson–Walker space-time with constant scalar curvature
Authors: Molinari Luca Guido , Mantica Carlo Alberto
Published: February 2019

The Ricci tensor of a Robertson–Walker (RW) space-time is here specified by requiring constancy of the scalar curvature and a vanishing spatial curvature. By entering this Ricci tensor in Einstein’s equations (without cosmological constant), the cosmological fluid shows a transition from a pure radiation to a Lambda equation of state. In other words, the RW geometry with constant scalar curvature and flat space fixes the limit values [Formula: see text] and [Formula: see text], without any hypothesis on the cosmological fluid. The value of the scalar curvature fixes the time-scale for the transition.

For this reason, we investigate the ‘toy-universe’ with Hubble parameter [Formula: see text] and temperature [Formula: see text][Formula: see text]K. The model predicts an age of the universe in the range 7.3–13.7[Formula: see text]Gyr.
Asymptotic solution for expanding universe with matter-dominated evolution
Authors: Mijajlović Žarko , Pejović Nadežda , Radović Viktor
Published: February 2019

We applied the theory of regularly varying (RV) functions to the analysis of the cosmological parameters for the [Formula: see text]CDM model with the matter-dominated evolution. Carroll et al. proved in 1992 that for this type of universe with the curvature [Formula: see text], the expression [Formula: see text] ([Formula: see text] is the Hubble parameter) depends solely on the density parameter [Formula: see text]. Using this result, we infer for such universe the complete asymptotics of all main cosmological parameters. More specifically, the following is derived. If the limit [Formula: see text] does exist and [Formula: see text], then the cosmological constant [Formula: see text] is equal to [Formula: see text]. If [Formula: see text], then for the expansion scale factor [Formula: see text] of a flat universe, we have [Formula: see text]. On the other hand, if the limit [Formula: see text] does not exist, then [Formula: see text] bounces between two power functions and therefore has infinitely many flexion points. Hence, the deceleration parameter in this case changes the sign infinitely many times.
Solving fractional diffusion equations by Sinc and radial basis functions
Authors: Mohammadi Rick Solmaz , Rashidinia Jalil
Published: February 2019

In this study, we approximate the solution of the fractional diffusion equations based on Gaussian radial basis function (GRBF). Our approach is based on the Caputo fractional derivative and the combination of GRBF and Sinc function, here the GRBF direct and GRBF-QR methods are developed. The Sinc quadrature rule combined with double exponential transformation (DE) has been used to approximate the fractional integral. Three examples have been considered to test the presented methods, we compared the results to verify the effectiveness of the presented methods against recent existing methods diven by [A radial basis functions method for fractional diffusion equations, J. Comput. Phys. 238 (2013) 71–81; An efficient Chebyshev-tau method for solving the space fractional diffusion equations, Appl. Math. Comput. 224 (2013) 259–267; A tau approach for solution of the space fractional diffusion equations, Comput. Math. Appl. 62 (2011) 1135–1142], and also conclude that GRBF-QR-Sinc method demonstrates better accuracy.
The Effectiveness of Urban Irrigation Day Restrictions in California
Authors: Hayden Hanna , Tsvetanov Tsvetan
Published: February 2019

We analyze the impact of restricting outdoor irrigation using monthly data from 408 urban water suppliers in California during the final years of the 2012–2017 drought. Our estimates suggest that assigning an additional no-irrigation day per week leads to a decrease in average monthly residential water consumption by approximately 0.8 gallons per capita-day. There is substantial heterogeneity in this impact. First, the marginal effect of a stricter irrigation policy varies depending on the existing level of outdoor watering restrictions — while initial restrictions lead to considerable conservation gains, tightening these measures further does not bring additional gains unless 6 weekly no-irrigation days are implemented. Furthermore, the policy is more effective in areas where residential water use represents a larger share of total urban water consumption and areas which perform better at reaching the 25% state conservation target.
WEATHER AND CLIMATE AS EVENTS: CONTRIBUTIONS TO THE PUBLIC IDEA OF CLIMATE CHANGE
Authors: STEWART ALAN E. , OH JUNGSU
Published: February 2019

One aspect of the psychology of weather and climate concerns the multiple meanings that may be associated with weather and climate as event. Atmospheric scientists and journalists have increasingly described both weather and climate as event. In this paper, the authors documented the increasing use of weather and climate as events in the scholarly literature of the American Meteorological Society and in newspaper articles over time. The authors also conducted pathfinder network scaling analyses with event-related terms to assess the meanings of events in academic and journalistic writing. The analyses suggested four contexts of event meanings: (1) study of ordinary weather or climate occurrences, (2) the study and attribution of severe and extreme weather, (3) societal impacts of weather, and (4) the public lexicon. Communicating about weather and climates as event contributes to the development and evolution of the public idea of climate change. The burgeoning of event in discourse contributes to the public idea of climate change in at least three ways: (1) events contribute specificity to the more general idea of climate change; (2) events contribute experientiality of climate change, and (3) events contribute exemplification to the public idea of climate change to the extent that weather events can be attributed to climate change.
Isolation Modeling and Analysis Based on Mobility
Authors: Jiang Jian-Min , Zhu Huibiao , Li Qin , Zhao Yongxin , Hong Zhong , Zhang Shi , Gong Ping
Published: February 2019

In a mobile system, mobility refers to a change in position of a mobile object with respect to time and its reference point, whereas isolation means the isolation relationship between mobile objects under some scheduling policies. Inspired by event-based formal models and the ambient calculus, we first propose the two types of special events, entering and exiting an ambient, as movement events to model and analyze mobility. Based on mobility, we then introduce the notion of the isolation of mobile objects for ambients. To ensure the isolation, a priority policy needs to be used to schedule the movement of mobile objects. However, traditional scheduling policies focus on task scheduling and depend on the strong hypothesis: The scheduled tasks are independent—that is, the scheduled tasks do not affect each other. In a practical mobile system, mobile objects and ambients interact with each other. It is difficult to separate a mobile system into independent tasks. We finally present an automatic approach for generating a priority scheduling policy without considering the preceding assumption. The approach can guarantee the isolation of the mobile objects for ambients in a mobile system. Experiments demonstrate these results.
Status Quo in Requirements Engineering
Authors: Wagner Stefan , Fernández Daniel Méndez , Felderer Michael , Vetrò Antonio , Kalinowski Marcos , Wieringa Roel , Pfahl Dietmar , Conte Tayana , Christiansson Marie-Therese , Greer Desmond , Lassenius Casper , Männistö Tomi , Nayebi Maleknaz , Oivo Markku , Penzenstadler Birgit , Prikladnicki Rafael , Ruhe Guenther , Schekelmann André , Sen Sagar , Spínola Rodrigo , Tuzcu Ahmed , Vara Jose Luis De La , Winkler Dietmar
Published: February 2019

Requirements Engineering (RE) has established itself as a software engineering discipline over the past decades. While researchers have been investigating the RE discipline with a plethora of empirical studies, attempts to systematically derive an empirical theory in context of the RE discipline have just recently been started. However, such a theory is needed if we are to define and motivate guidance in performing high quality RE research and practice.

We aim at providing an empirical and externally valid foundation for a theory of RE practice, which helps software engineers establish effective and efficient RE processes in a problem-driven manner.

We designed a survey instrument and an engineer-focused theory that was first piloted in Germany and, after making substantial modifications, has now been replicated in 10 countries worldwide. We have a theory in the form of a set of propositions inferred from our experiences and available studies, as well as the results from our pilot study in Germany. We evaluate the propositions with bootstrapped confidence intervals and derive potential explanations for the propositions.

In this article, we report on the design of the family of surveys, its underlying theory, and the full results obtained from the replication studies conducted in 10 countries with participants from 228 organisations. Our results represent a substantial step forward towards developing an empirical theory of RE practice. The results reveal, for example, that there are no strong differences between organisations in different countries and regions, that interviews, facilitated meetings and prototyping are the most used elicitation techniques, that requirements are often documented textually, that traces between requirements and code or design documents are common, that requirements specifications themselves are rarely changed and that requirements engineering (process) improvement endeavours are mostly internally driven.

Our study establishes a theory that can be used as starting point for many further studies for more detailed investigations. Practitioners can use the results as theory-supported guidance on selecting suitable RE methods and techniques.
Genetic, Functional, and Immunological Study of ZnT8 in Diabetes
Authors: Huang Qiong , Du Jie , Merriman Chengfeng , Gong Zhicheng
Published: February 2019

Zinc level in the body is finely regulated to maintain cellular function. Dysregulation of zinc metabolism may induce a variety of diseases, e.g., diabetes. Zinc participates in insulin synthesis, storage, and secretion by functioning as a “cellular second messenger” in the insulin signaling pathway and glucose homeostasis. The highest zinc concentration is in the pancreas islets. Zinc accumulation in cell granules is manipulated by ZnT8, a zinc transporter expressed predominately in pancreatic α and β cells. A common ZnT8 gene (SLC30A8) polymorphism increases the risk of type 2 diabetes mellitus (T2DM), and rare mutations may present protective effects. In type 1 diabetes mellitus (T1DM), autoantibodies show specificity for binding two variants of ZnT8 (R or W at amino acid 325) dictated by a polymorphism in SLC30A8. In this review, we summarize the structure, feature, functions, and polymorphisms of ZnT8 along with its association with diabetes and explore future study directions.
Functionally Fitted Block Method for Solving the General Oscillatory Second‐Order Initial Value Problems and Hyperbolic Partial Differential Equations
Authors: Jator S. N. , Ngwane F. F. , Kirby N. O.
Published: February 2019

We present a block hybrid functionally fitted Runge–Kutta–Nyström method (BHFNM) which is dependent on the stepsize and a fixed frequency. Since the method is implemented in a block‐by‐block fashion, the method does not require starting values and predictors inherent to other predictor‐corrector methods. Upon deriving our method, stability is illustrated, and it is used to numerically solve the general second‐order initial value problems as well as hyperbolic partial differential equations. In doing so, we demonstrate the method’s relative accuracy and efficiency.
Arabic Sentiment Classification Using Convolutional Neural Network and Differential Evolution Algorithm
Authors: Dahou Abdelghani , Elaziz Mohamed Abd , Zhou Junwei , Xiong Shengwu
Published: February 2019

In recent years, convolutional neural network (CNN) has attracted considerable attention since its impressive performance in various applications, such as Arabic sentence classification. However, building a powerful CNN for Arabic sentiment classification can be highly complicated and time consuming. In this paper, we address this problem by combining differential evolution (DE) algorithm and CNN, where DE algorithm is used to automatically search the optimal configuration including CNN architecture and network parameters. In order to achieve the goal, five CNN parameters are searched by the DE algorithm which include convolution filter sizes that control the CNN architecture, number of filters per convolution filter size (NFCS), number of neurons in fully connected (FC) layer, initialization mode, and dropout rate. In addition, the effect of the mutation and crossover operators in DE algorithm were investigated. The performance of the proposed framework DE-CNN is evaluated on five Arabic sentiment datasets. Experiments’ results show that DE-CNN has higher accuracy and is less time consuming than the state-of-the-art algorithms.
Early Peritoneal CC Chemokine Production Correlates with Divergent Inflammatory Phenotypes and Susceptibility to Experimental Arthritis in Mice
Authors: Rossato Cristiano , Albuquerque Layra Lucy , Katz Iana Suly Santos , Borrego Andrea , Cabrera Wafa Hanna Koury , Spadafora-Ferreira Mônica , Ribeiro Orlando Garcia , Starobinas Nancy , Ibañez Olga Martinez , De Franco Marcelo , Jensen José Ricardo
Published: February 2019

The inflammatory and autoimmune events preceding clinical symptoms in rheumatoid arthritis (RA) and other autoimmune diseases are difficult to study in human patients. Therefore, animal models that share immunologic and clinical features with human RA, such as pristane-induced arthritis (PIA), are valuable tools for assessing the primordial events related to arthritis susceptibility. PIA-resistant HIII and susceptible LIII mice were injected i.p. with pristane, and peritoneal lavage fluid was harvested in the early (7 days) and late (35 days) preclinical phases of PIA. Chemokine and cytokine levels were measured in lavage supernatant with ELISA, peritoneal inflammatory leukocytes were immunophenotyped by flow cytometry, and gene expression was determined by qRT-PCR. Leukocyte recruitment was quantitatively and qualitatively divergent in the peritoneum of HIII and LIII mice, with an early increase of CC chemokines (CCL2/CCL3/CCL5/CCL12/CCL22) in the susceptible LIII strain. Also, cytokines such as IL-12p40, IL-23, and IL-18 were elevated in LIII mice while IL-6 was increased in HIII animals. The results show that an early peritoneal CC chemokine response is an important feature of arthritis susceptibility and defines potential biomarkers in this model.
Chemical Functionalization of Helical Carbon Nanotubes: Influence of Sonication Time and Concentrations of Sulfuric and Nitric Acids with 3 : 1 Mixing Ratio
Authors: Taklimi Sean R. , Ghazinezami Ali , Askari Davood
Published: February 2019

Carbon nanotubes (CNTs) with straight geometries have been widely studied for various engineering applications, and they are often treated or functionalized to improve their effectiveness, depending on their role and expected performance. However, helical configurations of CNTs (HCNTs) have not been sufficiently investigated, especially in their functionalized states for high-performance nanocomposite applications. The coil-shaped geometry of these HCNTs increases the mechanical entanglement of these nanotubes with a host resin system when they are used as reinforcements. This consequently has the potential to improve the mechanical, thermal, electrical, and magnetic properties of the polymeric matrix systems. A uniform dispersion of CNTs in the resin plays an important role in obtaining improved and consistent properties in the final nanocomposite part. To improve the homogeneous dispersion (individual suspension) of these nanotubes in the host resin and to enhance their interactions/bonds with the resin molecules, the surface of these nanotubes should be modified. This study investigates a sonication method for chemical functionalization of HCNTs using a mixture of sulfuric and nitric acids with 3 to 1 mixing ratio [3 : 1], and it evaluates the effects of acid concentrations and sonication time on the severity of the functionalization process. To evaluate the effectiveness of the process parameters, the functionalized HCNTs (FHCNTs) were examined using several characterization instruments and techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), visual dispersion test, and Raman spectroscopy. The characterization results confirmed that the changes in process parameters were mostly effective and the atomic structures of the functionalized HCNTs were successfully altered. All FHCNT samples demonstrated higher dispersion uniformity, increase in Raman ID/IG ratios, and changes in the FTIR spectra compared to the pristine HCNTs. Most of the FHCNTs had a reduction in crystallinity, which was consistent with our expectation that functionalization generates more defects on the surface structure of HCNTs, thus leading to a lower intensity of the graphitic peak. The largest reduction in crystallinity was seen for HCNTs treated with a 16 molarity acidic solution; therefore, the HCNTs that were treated with lower molarity acids could be used for further studies and explored for their effective applications in improving the mechanical, thermal, and electrical properties of polymeric nanocomposites.
Generalized Out-of-Plane Equilibrium Points in the Frame of Elliptic Restricted Three-Body Problem: Impact of Oblate Primary and Luminous-Triaxial Secondary
Authors: Hussain Aminu Abubakar , Umar Aishetu
Published: February 2019

This paper studies the motion of a third body near the 1st family of the out-of-plane equilibrium points, L6,7, in the elliptic restricted problem of three bodies under an oblate primary and a radiating-triaxial secondary. It is seen that the pair of points (ξ0,0,±ζ0) which correspond to the positions of the 1st family of the out-of-plane equilibrium points, L6,7, are affected by the oblateness of the primary, radiation pressure and triaxiality of the secondary, semimajor axis, and eccentricity of the orbits of the principal bodies. But the point ±ζ0 is unaffected by the semimajor axis and eccentricity of the orbits of the principal bodies. The effects of the parameters involved in this problem are shown on the topologies of the zero-velocity curves for the binary systems PSR 1903+0327 and DP-Leonis. An investigation of the stability of the out-of-plane equilibrium points, L6,7 numerically, shows that they can be stable for 0.32≤μ≤0.5 and for very low eccentricity. L6,7 of PSR 1903+0327 and DP-Leonis are however linearly unstable.
Free Vibrations with Large Amplitude of Axially Loaded Beams on an Elastic Foundation Using the Adomian Modified Decomposition Method
Authors: Adair Desmond , Ibrayev Askar , Tazabekova Alima , Kim Jong R.
Published: February 2019

Analytical solutions describing free transverse vibrations with large amplitude of axially loaded Euler–Bernoulli beams for various end restrains resting on a Winkler one‐parameter foundation are obtained using the Adomian modified decomposition method (AMDM). The AMDM allows the governing equation to become a recursive algebraic equation, and, after some additional simple mathematical operations, the equations can be cast as an eigenvector problem whose solution results in the calculation of natural frequencies and corresponding closed‐form series solution of the mode shapes. Important to the use of the Adomian modified decomposition method is the treatment of the nonlinear Fredholm integral coefficient, which forms part of the governing equation. In addition to the calculation of natural frequencies and mode shapes, investigations are made of the effects on the free vibrations of the Winkler parameter and of increasing the axial loading.
Jet Milling as an Alternative Processing Technique for Preparing Polysulfone Hard Nanocomposites
Authors: Llorente Amaia , Serrano Berna , Baselga Juan , Gedler Gabriel , Ozisik Rahmi
Published: February 2019

This work describes how a solid-state blending method such as jet milling can be used to successfully prepare polysulfone (PSU)/γ-alumina nanocomposites. For comparison purposes, conventional melt extrusion was used as well. Morphological analysis revealed how jet mill blending allows obtaining well-dispersedγ-alumina nanoparticles within a polysulfone matrix without any surface treatment, with an important decrease of particle size promoted by the breakup of agglomerates and aggregates due to the particle-particle impacts during processing, which was not observed in the extruded nanocomposites. DSC analysis demonstrated that jet-milling processing promotedTgenhancements with alumina addition, while TGA experiments confirmed the increment of thermal stability of the nanocomposites prepared by jet milling when compared with the composites prepared by extrusion. The tensile tests showed that ductility remains at a high value for milled nanocomposites, which agreed with the fracture surface images revealing large plastic deformation as a function of the alumina content. This comparative study indicates that the dispersion of nanoparticles in PSU was more homogeneous, with smaller nanoparticles when preparing nanocomposites using jet milling, showing a strong correlation with the enhanced final properties of the nanocomposites.
Position Estimation Based on Grid Cells and Self-Growing Self-Organizing Map
Authors: Li Baozhong , Liu Yanming , Li Hailin
Published: February 2019

As the basis of animals’ natal homing behavior, path integration can continuously provide current position information relative to the initial position. Some neurons in freely moving animals’ brains can encode current positions and surrounding environments by special firing patterns. Research studies show that neurons such as grid cells (GCs) in the hippocampus of animals’ brains are related to the path integration. They might encode the coordinate of the animal’s current position in the same way as the residue number system (RNS) which is based on the Chinese remainder theorem (CRT). Hence, in order to provide vehicles a bionic position estimation method, we propose a model to decode the GCs’ encoding information based on the improved traditional self-organizing map (SOM), and this model makes full use of GCs’ firing characteristics. The details of the model are discussed in this paper. Besides, the model is realized by computer simulation, and its performance is analyzed under different conditions. Simulation results indicate that the proposed position estimation model is effective and stable.
Effect of Prior Rolling on Microstructures and Property of Diffusion-Bonded Mg/Al Alloy
Authors: Ding Yunlong , Shi Jialian , Ju Dongying
Published: February 2019

In this study, magnesium alloy AZ91, which was cast by double roll casting system, was rolled by a rolling mill. Then, rolled magnesium alloy and magnesium alloy without being rolled were, respectively, welded with aluminum alloy 6061 by diffusion bonding method. Furthermore, annealing process was applied to refine the microstructure and improve mechanical property. The microstructure and elemental distribution of diffusion zone were investigated with a scanning electron microscope (SEM), an electron probe micro analyzer (EPMA), and a transmission electron microscope (TEM). In addition, hardness and tensile strength were measured. When cast magnesium alloy was used, the width of diffusion layers was wider than that with rolled magnesium alloy. And the width increased with the increasing annealing temperatures. Element distribution of specimens with annealing was more uniform than that did not undergo annealing process. Furthermore, tensile strength turns to be strongest after annealing at 250°C. And the strength of the specimens with rolled magnesium alloy was stronger than that with cast magnesium alloy which was not rolled.
Evaluation Model of Generation Dispatching Optimization considering Participation of Electricity Retailers
Authors: Yu Xiaobao , Tan Zhongfu
Published: February 2019

The sales aspect of electricity reform is one of the focuses of current reform in China. Independent retailers are involved in the purchase of electricity, which is a sign of a mature electricity market. With the increasing degree of market opening, it is expected to become an important link between the generation side and demand side, and its degree of participation will directly affect the benefits of the demand response. From the analysis of the operation pattern of future electricity retailers that are involved in optimal generation dispatching, the load‐calculation model of the customer response and the dispatching model of electricity retailers involved in generation are established. Then, based on the principle of dynamics, a comprehensive assessment model is established. The results show that customers’ response to electricity retailers involved in the generation dispatch can improve the load rate by about 4%. The overall efficiency of various stakeholders is positive, and the investment cost of the government environmental management is gradually decreased.
Scanning Microscopy Techniques as an Assessment Tool of Materials and Interventions for the Protection of Built Cultural Heritage
Authors: Moropoulou Antonia , Zendri Elisabetta , Ortiz Pilar , Delegou Ekaterini T. , Ntoutsi Ioanna , Balliana Eleonora , Becerra Javier , Ortiz Rocío
Published: February 2019

Scanning microscopy techniques have emerged as powerful scientific tools for analysing materials of architectural or archaeological interest, since the commercialization of the first scanning electron microscopy instrumentation in the early 60s. This study is aimed at reviewing and highlighting the significance of several scanning microscopy techniques employed in the protection of built heritage. The diffusion of scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis (SEM-EDX) is proven to be the widest among the available scanning microscopy techniques, while transmission electron microscopy (TEM) applications are steadily present in the field of built heritage protection. The building material characterization, the weathering mechanism investigation, and the development of compatible and performing conservation materials are some major research areas where the application of the aforementioned techniques is discussed. The range of techniques, along with aspects of instrumentation and sample preparation are, also, considered.
Alleviation of Cartilage Destruction by Sinapic Acid in Experimental Osteoarthritis
Authors: Cai Dawei , Huff Thomas W. , Liu Jun , Yuan Tangbo , Wei Zijian , Qin Jian
Published: February 2019

Sinapic acid (SA) modulates the nuclear factor-erythroid 2-related factor 2 (Nrf2) signaling pathway in chondrocytes. In order to test the hypothesis that SA is protective against the development of osteoarthritis (OA), primary mouse chondrocytes were treated in vitro with SA and the promoter transactivation activity of heme oxygenase 1 (HO-1), nuclear translocation of Nrf2, and protein expression of HO-1 were assayed. To test the hypothesis in vivo, a destabilization of the medial meniscus (DMM) model was used to induce OA in the knees of mice and SA was delivered orally to the experimental group. The chondrocytes were harvested for further analysis. The expression of HO-1 was similarly upregulated in cartilage from both the experimental mice and human chondrocytes from osteoarthritic knees. SA was found to enhance the promoter transactivation activity of heme oxygenase 1 (HO-1) and increase the expression of Nrf2 and HO-1 in primary chondrocytes. Histopathologic scores showed that the damage induced by the DMM model was significantly lower in the SA treatment group. The addition of a HO-1 inhibitor with SA did not show additional benefit over SA alone in terms of cartilage degradation or histopathologic scores. The expression of TNF-α, IL-1β, IL-6, MMP-1, MMP-3, MMP-13, ADAMTS4, and ADAMTS5 was significantly reduced both in vitro and in vivo by the presence of SA. Protein expressions of HO-1 and Nrf2 were substantially increased in knee cartilage of mice that received oral SA. Our results suggest that SA should be further explored as a preventative treatment for OA.
Influence of Water-Repellent Treatment with Silicon Resin on Properties of Concrete
Authors: Tian Yupeng , Wang Penggang , Zhao Tiejun , Ma Zhiming , Jin Zuquan , Zhao Haitao
Published: February 2019

Although studies on water-repellent properties of silicon resin (SR) on cement-based materials have received tremendous attention around the world in recent years, they mainly focus on individual properties of water-repellent concrete treated with SR such as strength and water permeability resistance. However, to date, a systematic and comprehensive investigation is missing. The current study therefore investigates the influence of SR on the durability properties of cementitious materials by adding SR emulsion into integral concrete mixture and coating concrete surface with SR. The microscopic and mechanical properties and the durability performance were tested on the integral SR water‐repellent concrete (C-ISR) and SR surface water-repellent concrete (C-SSR). The obtained results indicate that SR application has no impact on hydration reaction and corresponding composition of cement-based materials, while SR addition leads to a reduction in strength and early shrinkage of cement mortar because the added SR delays the hydration reaction. Water-repellent treatment via SR can significantly reduce the water permeability of concrete, which is more apparent for surface water-repellent treatment (SSR). Furthermore, the durability properties were investigated, and the results indicate that integral SR water-repellent treatment (ISR) possesses better properties than SSR, which suggests water-repellent treatment via surface coating as an effective means to improve concrete durability.
Heun-Type Solutions of the Klein-Gordon and Dirac Equations in the Garfinkle-Horowitz-Strominger Dilaton Black Hole Background
Authors: Dariescu Marina-Aura , Dariescu Ciprian , Stelea Cristian
Published: February 2019

We study the Klein-Gordon and the Dirac equations in the background of the Garfinkle-Horowitz-Strominger black hole in the Einstein frame. Using a SO(3,1)×U(1)-gauge covariant approach, as an alternative to the Newman-Penrose formalism for the Dirac equation, it turns out that these solutions can be expressed in terms of Heun confluent functions and we discuss some of their properties.
Size-Dependent Cytotoxicity and Genotoxicity of Silver Nanoparticles in Cochlear Cells In Vitro
Authors: Perde-Schrepler Maria , Florea Adrian , Brie Ioana , Virag Piroska , Fischer-Fodor Eva , Vâlcan Angela , Gurzău Eugen , Lisencu Cosmin , Maniu Alma
Published: February 2019

Silver nanoparticles (AgNPs) have been proven to have potent antibacterial properties, offering an attractive alternative to antibiotics in the treatment of several infections such as otitis media. Concerns have been raised though regarding their toxicity. There are few data regarding the toxic effects of AgNPs in cochlear cells. The aim of our study was to evaluate the effects of AgNPs of four sizes as a function of their size on HEI-OC1 cochlear cells and on HaCaT keratinocytes. The cells were treated with different concentrations of AgNPs. We evaluated silver uptake by atomic absorption spectroscopy and transmission electron microscopy (TEM), cytotoxicity with the alamarBlue test, ROS production with 2′,7′-dichloro-dihydro-fluorescein diacetate, and genotoxicity with the comet assay. Silver intracellular concentration increased proportionally with the incubation time and the size of the NPs. Silver uptake was higher in HEI-OC1 cells compared to HaCaT. While after 4 h exposure, only the 50 nm NPs were observed in both cell lines and only the 5 nm NPs were observed in the HaCaT cells, after 24 h, nanoparticles of all sizes could be visualized in both cell lines. The cells showed signs of distress: vacuolizations, autophagosomes, signs of apoptosis, or cellular debris. AgNPs of all sizes reduced viability proportionally with the concentration, HEI-OC1 cells being more affected. The toxicity of AgNPs decreased with the nanoparticle size, and ROS production was dose and size dependent, mainly in the cochlear cells. Genotoxicity assessed by comet assay revealed a higher level of DNA lesions in HEI-OC1 cells after treatment with small-sized AgNPs. The perspective of using AgNPs in the treatment of otitis media, although very attractive, must be regarded with caution: cochlear cells proved to be more sensitive to the toxic effect of AgNPs compared to other cell lines. Potential treatments must be tailored specifically, choosing NPs with minimum toxicity towards auditory cells.
Assessment of Meat Quality and Shelf Life from Broilers Fed with Different Sources and Concentrations of Methionine
Authors: Albrecht Antonia , Hebel Martin , Heinemann Céline , Herbert Ulrike , Miskel Dennis , Saremi Behnam , Kreyenschmidt Judith
Published: February 2019

A trial with different concentrations of DL-methionine (DLM) and DL-2-hydroxy-4-methylthiobutanoic acid (DL-HMTBA) in broiler feed was performed to investigate their effect on the meat quality parameters and the shelf life of breast fillet. In total, fillets from 210 male broiler chickens (Ross 308) were tested in seven groups with 30 animals each. Three different concentrations (0.04, 0.12, and 0.32%; on an equimolar basis) of either DLM or DL-HMTBA were added to a basal diet, summing up to seven treatment groups. After slaughter, fillets were packed aerobically and stored at 4°C. The investigated parameters comprised measurements of microbial as well as physicochemical parameters, such as pH, drip loss, cooking loss, and color measurements. Additionally, sensory investigations were conducted and shelf life was calculated. Mean pH values were between 6.1 and 6.4. Drip loss values were low, with mean values below 0.4%. The cooking loss ranged between 22% and 28% on average. The fillets showed a normal initial microbial quality (2.5 log10 cfu/g) and spoilage process with microbial counts of 8.5 log10 cfu/g at the end of storage. The study revealed a significant influence of methionine supplementation on the quality of broiler breast meat in comparison with the basal group. Methionine supplementation led to higher pH values and a higher water binding. Higher concentrations of methionine had a positive influence on the water-holding capacity by lowering the cooking loss. The L∗ value showed a significant negative correlation to the methionine concentration supplemented. No differences in physicochemical as well as sensory parameters could be detected between both methionine sources. The fillets showed a normal sensory spoilage process and a shelf life of 6 d. White striping was positively correlated to fillet weight as well as color values and significantly affected the Purchase Decision, the sensory investigation, and thus the shelf life of the samples.
A Discrete Element Model for Damage and Fatigue Crack Growth of Quasi-Brittle Materials
Authors: Gao Xiaofeng , Koval Georg , Chazallon Cyrille
Published: February 2019

The repeatedly applied low-intensity loads would lead to the damage and fatigue crack growth of mechanical structures made of quasi-brittle materials. In numerical modelling, these two mechanisms are normally treated differently and separately; the damage is usually associated with nonlocal approaches, while the fatigue crack growth is related to the local stress intensity range at the crack tip. In this study, a discrete element model for damage and fatigue crack growth of quasi-brittle materials is proposed, which is able to model the damage and fatigue crack growth simultaneously in one single model. The proposed model achieves the implementation of a continuum damage model in a discrete element code, which is a helpful enrichment of this numerical method. The evaluation method of the stress intensity range during the damage evolution provides a way to couple both failure mechanisms. This feature allows crack initiation to be induced by localized damage and a progressive transition to a fracture behaviour with the crack propagation. Independent parameters for the fatigue damage model and fatigue crack growth model are admitted without any previous calibration. The numerical results are in good agreement with the theoretical predictions of damage and fracture mechanics, and intact and precracked samples are analysed under fatigue loading to show the consistent coexistence of fractured and damaged zones in a single model.
Influence of Degree of Dispersion of Noncovalent Functionalized Graphene Nanoplatelets on Rheological Behaviour of Aqueous Drilling Fluids
Authors: Ibrahim Arif , Ridha Syahrir , Amer Asna , Shahari Radzi , Ganat Tarek
Published: February 2019

Application of carbon nanomaterials in oil well drilling fluid has been previously studied and was found to enhance its filtration properties. There is a general consensus that addition of colloids in suspension will alter its rheology, i.e., carbon nanomaterials, in this research work; graphene nanoplatelets are hydrophobic materials, which require functionalisation to improve its dispersion in aqueous solution. However, different degrees of dispersion may vary the rheological properties behaviour of drilling fluid. The objective of this study was to characterize the colloidal dispersion of graphene nanoplatelets (GNP) in aqueous solution and its impact on the rheological properties behaviour of water-based drilling fluid. Dispersion of graphene nanoplatelets was achieved through noncovalent functionalisation by means of surfactant attachment. UV-visible spectroscopy was employed to analyze the dispersion of GNP in aqueous solution. The rheological test was carried out using a simple direct-indicating viscometer at six different speeds. Results revealed that the degree of dispersion of GNP using Triton X-100 was generally higher than both SDS and DTAB. Comparison between the rheological properties behaviour of drilling fluid with GNP dispersed using different surfactants shows little to no difference at low shear rates. At high shear rates, however, greater dispersion of GNP shows higher thinning properties while fluid with a low dispersion of GNP exhibited linear behaviour to thickening properties.
Study on the Dynamic Problems of Double‐Disk Rotor System Supported by Deep Groove Ball Bearing
Authors: Liu Yang , Han Jiyuan , Zhao Siyao , Meng Qingyu , Shi Tuo , Ma Hui
Published: February 2019

Aiming at the analysis of the dynamic characteristics of the rotor system supported by deep groove ball bearings, the dynamic model of the double‐disk rotor system supported by deep groove ball bearings was established. In this paper, the nonlinear finite element method is used combined with the structural characteristics of deep groove ball bearings. Based on the nonlinear Hertz contact theory, the mechanical model of deep groove ball bearings is obtained. The excitation response results of the rotor system nodes are solved by using the Newmark‐β numerical solution method combined with the Newton–Raphson iterative method. The vibration characteristics of the rotor system supported by deep groove ball bearings are studied deeply. In addition, the effect of varying compliance vibration (VC vibration) caused by the change in bearing support stiffness on the dynamics of the system is considered. The time domain and frequency domain characteristics of the rotor system at different speeds, as well as the influence of bearing clearance and bearing inner ring’s acceleration on the dynamics of the rotor system are analyzed. The research shows that the VC vibration of the bearing has a great influence on the motion of the rotor system when the rotational speed is low. Moreover, reasonable control of bearing clearance can reduce the mutual impact between the bearing rolling element and the inner or outer rings of the bearing and reduce the influence of unstable bearing motion on the vibration characteristics of the rotor system. The results can provide theoretical basis for the subsequent study of the nonlinear vibration characteristics of the deep groove ball bearing rotor system.
Motion Simulation of Ionic Liquid Gel Soft Actuators Based on CPG Control
Authors: Zhang Chenghong , He Bin , Ding An , Xu Shoulin , Wang Zhipeng , Zhou Yanmin
Published: February 2019

The ionic liquid gel (ILG), a new type of soft actuator material, is a mixture of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hydroxyethyl methacrylate (HEMA), diethoxyacetophenone (DEAP), and ZrO2 polymerized into a gel state under ultraviolet (UV) light irradiation. The soft actuator structure consists of a layer of ionic liquid polymer gel sandwiched between two layers of activated carbon capped with gold foil. The volume of the cationic BMIM+ in the ionic liquid BMIMBF4 is much larger than that of the anionic BF4−. When voltages are applied to both sides of the actuator, the anions and cations move toward the anode and cathode of the electrode, respectively, under the electric field. The volume of the ILG cathode side therefore expands, and the volume of the ILG anode side shrinks, hence bending the entire actuator toward the anode side. The Ogden model was selected as the hyperelastic constitutive model to study the mechanical properties of the ILG by nonlinear analysis. As the ILG is an ideal material for the preparation of a supercapacitor, the equivalent circuit of the ILG can be modeled by the supercapacitor theory to identify the transfer function of the soft actuator. The central pattern generator (CPG) control is widely used in the area of biology, and CPGs based on bioinspired control methods have attracted great attention from researchers worldwide. After the continuum soft actuator is discretized, the CPG-based bioinspired method can be used to control the soft robot drivers. According to the simulation analysis results, the soft actuator can be smooth enough to reach the specified location.
Coal Burst Induced by Horizontal Section Mining of a Steeply Inclined, Extra‐Thick Coal Seam and Its Prevention: A Case Study from Yaojie No. 3 Coal Mine, China
Authors: Wang Zhengyi , Dou Linming , Wang Guifeng
Published: February 2019

At present, coal bursts in working faces of steeply inclined coal seams (SICSs) have rarely been investigated, and current research focuses on the influences of roof breaking and instability of overlying structures in goaf on coal bursts; however, the stress state of coal masses in working faces being subjected to coal bursts is rarely researched. To overcome the above defects, a model for analysing stresses on coal masses in horizontal section of SICSs was established based on the coal burst that occurred in LW5521‐20, Yaojie No. 3 Coal Mine, Lanzhou, Gansu Province, China. Moreover, the mechanism underpinning such a coal burst in SICSs was analysed based on the superposition mechanism of dynamic and static loads. The results show that the side abutment pressure near the roof and floor under the horizontal sections of SICSs is asymmetrically distributed in the vertical direction in which the peak of side abutment pressure near the roof is closer to the working face and therefore is taken as the source of static loads for coal bursts in working faces. When the superimposed dynamic load caused by hanging roof breaking and high static load borne in the coal masses is larger than the critical load for coal burst inception, a coal burst will occur. Furthermore, the superimposed dynamic load induced by coal bursts on the support and the initial static load on the supports are larger than their limiting load, which leads to support collapse and eventually causes dynamic failure of the working face. The coal burst in working faces in horizontal sections of SICSs can be prevented by using deep‐hole presplit blasting in a hard roof, destress blasting in coal masses, and support optimisation of working faces, showing a favourable preventative effect.