A Novel Composite Coding Method for Incoherent Scatter Radar

Many modern ionospheric studies rely on incoherent scatter radars (ISR) since this kind of radar is able to detect various ionospheric parameters over very long ranges. The performance of ISR significantly depends on its coding system. In recent decades, a new type of coding system, which is the so-called composite coding, was presented. It used to be constructed by using a certain code to modulate alternating code to achieve better detection resolution and anti-noise performance for ISRs. In the present study, a new composite coding system was presented, which is constructed based on complementary codes and alternating codes. In this paper, the performance of the new composite code will be compared with that of several traditional codes to show that the new composite code can help to improve the detection performance of the ISR. According to the analysis based on the ambiguity function, the present composite coding system helps to improve the range resolution and detection range for ISR detections. In addition, numerical tests on anti-noise performance show that the complementary composite coding system has a good anti-noise performance and helps to reduce the necessary times of incoherent integration. As a result, the composite coding system can improve the time resolution.

HIGH ENERGY WIDE AREA BLUNT IMPACT OF COMPOSITE AIRCRAFT STRUCTURES PART B: TESTING AND INTERNAL DAMAGE MODES

Modern aircraft structures constructed from high strength laminated composite materials present a challenge in the detection of damage resulting from impact events. Broad-area contact from large sized or blunt radius objects furthermore create conditions in which significant internal damage can result, while leaving low (or even no) externally visible indications of damage being present. Composite fuselage structures subjected to high energy wide area blunt impact (HEWABI) sources have been studied. These impact sources act over a wide area and can possibly damage multiple internal structural elements. HEWABI sources of concern are generally heavy ground service equipment (GSE) such as belt loaders, cargo loaders, catering trucks, etc., which have soft rubber/elastomeric bumper-type pads mounted at locations where the GSE could contact the aircraft. Of particular interest in this study is the formation of damage in composite frame and shear tie components during HEWABI events occurring near the passenger floor joint. Carbon/epoxy composite test specimens reflecting modern composite fuselage features were designed and fabricated having continuous shear ties and representative stiffness interaction between the floor beam and circumferential frame members. Quasi-static and slow speed tests (representing impact) conducted using rubber bumper faced indentors developed significant internal damage to internal components. Specifically, fiber failures and large-size crack formation in shear ties, frames, and stringers occurred with low/no external observability in the external skin. A clear quantitative understanding of damage modes and damage location that could result from HEWABI events is important for establishing damage size criteria in the evaluation of a structure’s residual strength and damage tolerance capability.

Innovative Biochar-Based Composite Fibres from Recycled Material

Carbon materials are becoming crucial in several industrial sectors. The drawbacks of these materials include their high cost and oil-based essence. In recent years, recycled materials have become possible alternative sources of carbon with several advantages. Firstly, the production of this alternative source of carbon may help to reduce biomass disposal, and secondly, it contributes to CO2 sequestration. The use of carbon derived from recycled materials by a pyrolysis treatment is called biochar. Here, we present composite materials based on different biochar filler contents dispersed in several thermoplastic polymer matrixes. Electrical conductivity and tensile break strength were investigated together with the material characterisation by DTA/TGA, XRD, and scanning electron microscopy (SEM) imaging. Materials with good flexibility and electrical conductivity were obtained. The local ordering in composites resembles both biochar and polymer ordering. The similarity between biochar and carbon nanotubes’ (CNTs) XRD patterns may be observed. As biochar is highly cost-effective, the proposed composites could become a valid substitute for CNT composites in various applications.

CH₄ and N₂O fluctuations during the penultimate deglaciation

Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 000 years. Reconstructions of millennial- to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of ∼100 years. Our data permit the identification of centennial-scale fluctuations during the transition from glacial to interglacial levels. At ∼134 000 and ∼129 000 years before present (hereafter ka), both CH4 and N2O increased on centennial timescales. These abrupt rises are similar to the fluctuations associated with the Dansgaard–Oeschger events identified in the last glacial period. In addition, gradually rising N2O levels at ∼130 ka resemble a pattern of increasing N2O concentrations on millennial timescales characterizing the later part of Heinrich stadials. Overall, the events in CH4 and N2O during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation and glacial cycle, suggesting that the processes leading to changes in emission during the transitions were similar but their timing differed.

CH₄ and N₂O fluctuations during the penultimate deglaciation

Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 thousand years. Reconstructions of millennial to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of about ~ 100 years. Our data permit the identification of centennial-scale fluctuations standing out of the overall transition to interglacial levels. These features occurred in concert with reinvigorations of the Atlantic Meridional Overturning Circulation (AMOC) and northward shifts of the Intertropical Convergence Zone. The abrupt CH4 and N2O rises at about ~ 134 and ~ 128 thousand of years before present (hereafter ka BP) are assimilated to the fluctuations accompanying the Dansgaard–Oeschger events of the last glacial period, while rising N2O levels at ~ 130.5 ka BP are assimilated to a pattern of increasing N2O concentrations that characterized the end of Heinrich stadials. We suggest the 130.5-ka event to be driven by a partial reinvigoration of the AMOC. Overall, the CH4 and N2O fluctuations during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation. However, trace gas responses may differ for similar type of climatic events, as exemplified by the reduced amplitude and duration of the 134-ka event compared to the fluctuations of the Bølling–Allerød during the last deglaciation.

Microstructure, wear and corrosion characteristics of Cu matrix reinforced SiC–graphite hybrid composites

The aim of the present study is to investigate the effect of SiC-graphite reinforcement on the properties of pure copper. Copper matrix composites with SiC-graphite reinforcement (0, 2.5,5, 7.5 and 10 wt.%) were prepared by stir casting process. Microstructure, phase, density, hardness and wear rate of prepared samples have been investigated. X-ray diffraction revealed that there is no intermediate phase formation between the reinforcement and matrix as a result of interfacial bonding between them. Microstructure study shows the uniform distribution of SiC-graphite particles in the Cu-matrix. Mechanical and corrosion properties of these Cu matrix MMCs were found to be dependent on the reinforcement content. Hardness was found to decrease with the addition of graphite due to its soft nature. Composite containing 5 wt.% reinforcement has shown minimum wear rate and maximum corrosion resistance. It is expected that the present composite will be useful for thermal management applications especially in heat exchangers.

Composite Indicators for Measuring the Popularity of Portugal and Its Tourism Regions Using Google Trends

The aim of this chapter is to present composite indicators that contribute to the understanding of online interest of Portuguese people for domestic tourism at national and regional level and by characteristic tourism product in each region of the country. For the construction of the composite indicators, data was collected for one year using the Google Trends tool, for a set of a priori defined search terms representative of the Portugal destination and its regions. The composite indicators result from the average weighting of seven primary indicators, composed of fifteen sub-indicators, which were proposed based on the conceptual framework of the Tourism Satellite Account. The results indicate that the interest of the Portuguese people by Portugal and its regions shows a seasonal behavior whose accent varies according to the tourism region, as well as the characteristics tourism products.

Effect of aluminum nitride concentration on different physical properties of low density polyethylene based nanocomposites

In this study, blends of low-density polyethylene (LDPE)/aluminum nitride (AlN) ceramic nanocomposites have been prepared through melt blending technique. Increased loading of AIN leads to reduction in tensile properties but improvement in rheological property (storage modulus). The rheological behavior tends to become unique at higher frequencies (≥10 rad/s). Differential scanning calorimetry (DSC) results show that the total crystallinity has decreased with the increase in AlN loading in the composites. It is seen that there is an improvement in electrical conductivity, dielectric constant, and flammability properties with the addition of AlN in the nanocomposites. The experimental data of tensile modulus, electrical conductivity, and dielectric constant have been fitted with some available theoretical models to check the models’ applicability for the present composite systems. Results show that only Nicolais-Nicodemo model, McCullough model, and Rahaman-Khastgir model are applicable for predicting the tensile modulus, electrical conductivity, and dielectric constant of the composites, respectively.

Influence of some dental biomaterials on periodontal tissue

Dental biomaterials are designed to restore form and function of the dental tissue, to protect the remaining tissue and to create a bond between the dental surface and the restorative material. Due to their proximity to dental structures and oral mucosa, dental biomaterials must fulfil the requirements of biocompatibility and biological durability. The research in the field is focused on achieving these requirements by developing new highly performant biomaterials. But at present, composite materials still present some drawbacks like the polymerisation shrinkage associated to the curing process that leads to the adhesive interface breakdown and marginal microleakage. Composite materials may release substances into the oral environment during setting and later as a result of material degradation. Different side effects of composite materials and their components have been reported i.e. cytotoxic, teratogenic, carcinogenic, mutagenic or genotoxic. Despite the developments in the field, at present no „ideal“ restorative biomaterial with similar characteristics with the natural teeth and completely biocompatible is available. However, the application of strict clinical protocols may improve the above mentioned shortcomings.

REORIENTATION OF FIBRES AND LOCAL MECHANISMS OF DEFORMATION IN A WOOD-INSPIRED COMPOSITE

This paper investigates the reorientation of fibres and local mechanisms of deformation in a composite material inspired by the mechanics and structure of wood cell-walls. The mechanical response of the material is calculated under tensile loading conditions by means of the computational homogenisation of a two-dimensional representative volume element (RVE) of material. Here, the fibres are represented by a periodic alternation of alumina and magnesium alloy fractions, embedded in a soft epoxy matrix. In order to validate the present multi-scale framework, we compare our numerical prediction for the reorientation of fibres in the wood cell-wall composite with experimental data, finding a good agreement for a wide range of strains. Numerical simulations show that the model is able to describe the reorientation of fibres and the different stages of local deformation and failure in the proposed wood-inspired material. Furthermore, we assess a simple expression to calculate the reorientation of fibres and the in-plane Poisson's ratio of the present composite.