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A nanocomposite of magnetic hydroxyapatite was synthesized and tested as an adsorbent for the removal of copper (Cu (II)) and nickel (Ni(II)) from aqueous solution. The adsorbent was investigated using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy equipped with an Energy Dispersive Spectrometer (SEM/EDS), X-ray powder diffraction (XRD) and the Brunauer–Elmet–Teller nitrogen adsorption technique (BET-N 2 adsorption). Batch experiments were carried out to determine and compare the adsorption parameters of Fe 3 O 4 and its composite with hydroxyapatite. It was found that the adsorbent is nanostructured and has a specific surface area of 101.2 m 2  g −1 . The Langmuir adsorption isotherm was found to be an appropriate model to describe the adsorption processes, showing the adsorption capacities of Cu(II) and Ni(II) of 48.78 mg g −1 and 29.07 mg g −1 , respectively. In addition to the high adsorption capacity, the fully-adsorbed material could be easily separated from aqueous media using an external magnetic field. These results suggested that the utilization of new hydroxyapatite – Fe 3 O 4 nanocomposite for the removal of Cu(II) and Ni(II) is a promising method in water technology. [ABSTRACT FROM AUTHOR]

One of the current problems concerning the re-use of aluminium alloys is the recycling of aluminium alloys with increased content of iron. One of the recent trends is the processing by powder metallurgy, producing completely new grades of aluminium alloys. The aim of the present work was to test the properties of Al–Si–Fe alloy, which can be manufactured from the high-irony scrap, as a possible material for elevated temperature applications. Since chromium and nickel accompany the iron in the scrap when stainless steels are admixed, the effect of chromium and nickel on thermal stability and mechanical properties at room and elevated temperature was also studied. Al–Si–Fe–X alloys were rapidly solidified by using melt spinning technique. The rapidly solidified ribbons were pulverized by planetary ball mill and the obtained powders were used for compaction by means of Spark Plasma Sintering. It was found that nickel improves the thermal stability as well as the mechanical properties at the elevated temperature. On the other hand, the effect of chromium on the mechanical properties at elevated temperature was almost detrimental. [ABSTRACT FROM AUTHOR]

This work deals with a problem of paraxial analysis of optical systems for transformation of Gaussian beams. General equations describing the paraxial parameters of a two-element zoom system for transformation of a Gaussian beam are derived. It is shown that such a zoom lens has different kinematics with respect to classical zoom system designed for homocentric beams, which depends on the parameters of the transformed Gaussian beam. [ABSTRACT FROM AUTHOR]

The geoid is an equipotential surface of the static Earth's gravity field which plays a fundamental role in definition of physical heights related to the mean sea level (orthometric heights) in geodesy and which represents a reference surface in many geoscientific studies. Its determination with the cm-level accuracy or better, in particular over dry land, belongs to major tasks of modern geodesy. Traditional data and underlined theory have significantly been affected in recent years by rapid advances in observation techniques. This study reviews gradients of the disturbing gravity potential, both currently available and foreseen, and systematically discusses mathematical models for geoid determination based on gradient data. Fundamentals required for geoid definition and its estimation from measured potential gradients are shortly reviewed at the beginning of the text. Then particular mathematical models based on solutions to boundary-value problems of the potential theory, which include both integral transforms and integral equations, are formulated. Properties of respective integral kernel functions are demonstrated and discussed. With the new mathematical models introduced, new research topics are opened which must be resolved in order to allow for their full-fledged applicability in geoid modelling. Stochastic modelling is also discussed which estimates gradient spatial resolution and accuracy required for geoid modelling with the cm-level accuracy. Results of stochastic modelling suggest that the cm-geoid can be estimated using available gradient data if related problems, namely reduction of gradient data for gravitational effects of all masses outside the geoid and their downward continuation, are solved at the same level of accuracy. [ABSTRACT FROM AUTHOR]

Coercivity in rare-earth permanent magnets depends on the size and shape of magnetic grains. Recent experimental studies have revealed that, however, atomic scale structures around the grain-boundaries of magnets also play a crucial role to determine their coercivity. In this paper, we construct an effective spin model for the Nd 2 Fe 14 B structure based on first-principles calculations to describe atomistic magnetization dynamics of the magnetic grains, incorporating the information of the electronic states of the system. We find that the Nd ions located on the surfaces of the grains may have planar magnetic anisotropy, and that they can cause coercivity reduction. [ABSTRACT FROM AUTHOR]

The structure of Ni 8 Ti 5 was solved and refined from precession electron diffraction tomography data using dynamical refinement approach. It has trigonal symmetry R -3 m ( a = 12.24(5) Å, c = 15.33(5) Å) with a structure related to the structure of Ni 4 Ti 3 . The greatest challenge of the structure determination was the assignment of atomic types due to the proximity of scattering powers of Ti and Ni. Several approaches to determination of atom type distribution over atomic positions were used; (1) analysis of the Wyckoff position multiplicities, (2) refinement of displacement parameters, and (3) geometrical analysis of the structure and comparison with known structures. These approaches consistently pointed to one distribution, which was confirmed by a significant improvement of the refinement figures of merit. [ABSTRACT FROM AUTHOR]

In this article we discuss a regional recovery of gravity disturbances at the mean geocentric sphere approximating the Earth over the area of Central Europe from satellite gravitational gradients. For this purpose, we derive integral formulas which allow converting the gravity disturbances onto the disturbing gravitational gradients in the local north-oriented frame (LNOF). The derived formulas are free of singularities in case of r ≠ R . We then investigate three numerical approaches for solving their inverses. In the initial approach, the integral formulas are firstly modified for solving individually the near- and distant-zone contributions. While the effect of the near-zone gravitational gradients is solved as an inverse problem, the effect of the distant-zone gravitational gradients is computed by numerical integration from the global gravitational model (GGM) TIM-r4. In the second approach, we further elaborate the first scenario by reducing measured gravitational gradients for gravitational effects of topographic masses. In the third approach, we apply additional modification by reducing gravitational gradients for the reference GGM. In all approaches we determine the gravity disturbances from each of the four accurately measured gravitational gradients separately as well as from their combination. Our regional gravitational field solutions are based on the GOCE EGG_TRF_2 gravitational gradients collected within the period from November 1 2009 until January 11 2010. Obtained results are compared with EGM2008, DIR-r1, TIM-r1 and SPW-r1. The best fit, in terms of RMS (2.9 mGal), is achieved for EGM2008 while using the third approach which combine all four well-measured gravitational gradients. This is explained by the fact that a-priori information about the Earth’s gravitational field up to the degree and order 180 was used. [ABSTRACT FROM AUTHOR]

Third-order gradients of the gravitational potential (gravitational curvatures) have already found some applications in geosciences. Observability of these parameters, describing the Earth's gravitational field in a more complex way than any other currently available gravitational parameter, such as gravitational acceleration (first-order gradient) or gravitational (second-order) gradient, is currently discussed by physicists. Moreover, first designs of observational devices (sensors) have already been proposed. The spherical harmonic analysis and synthesis are the common tools used by geoscientists to study spectral properties of various functionals of the Earth's gravitational potential. However, the conventional spherical harmonic expansions of the gravitational curvatures in the local north-oriented reference frame have rather complicated forms that depend on the first-, second- and third-order derivatives of the associated Legendre functions. Moreover, some of these expansions also contain singular terms at the poles. In this paper, the conventional series are transformed to new simpler and non-singular forms based on relations between the associated Legendre functions and their derivatives. Numerical experiments demonstrate the applicability and correctness of the new expressions. [ABSTRACT FROM AUTHOR]

• The IUCN Red List of Ecosystems criteria were applied at the national scale. • 157 types of natural and semi-natural habitats of the Czech Republic were assessed. • Two habitats were Collapsed, 14 Critically Endangered, 33 Endangered, 33 Vulnerable. • Natural succession after abandonment, eutrophication and drought are major threats. • IUCN Red List of Ecosystems criteria are applicable in small countries or regions. The Red List of Habitats of the Czech Republic assesses the risk of collapse for 157 types of natural and semi-natural habitats defined in the second edition of the Habitat Catalogue of the Czech Republic. The assessment followed the guidelines for the IUCN Red List of Ecosystems as used in the European Red List of Habitats project, using the criteria of habitat reduction in quantity, restricted geographic distribution, and reduction in abiotic and biotic quality. Quantitative data for the assessment were partly taken from a detailed field habitat mapping at the national scale, and where no quantitative information was available, the values were estimated by summarizing independent judgements of 17 experts. In addition to the criteria involved in the Red List assessment, the experts also assessed various types of threatening factors and their importance for each habitat. Of 157 assessed habitats, 2 were Collapsed (CO), 14 Critically Endangered (CR), 32 Endangered (EN), 33 Vulnerable (VU), 30 Near Threatened (NT) and 46 Least Concern (LC). The largest proportion of CR + EN habitats was in the habitat group of springs and mires and in the group of wetlands. The threatening factors evaluated as the most important were successional changes after cessation of traditional management, eutrophication due to atmospheric nutrient deposition and pollution from agriculture, and increased drought in water-dependent habitats due to climate change or changes in local hydrological regime. The study shows that the IUCN criteria for Red List assessment of habitats, although developed for the global scale, are also applicable within small countries or regions. [ABSTRACT FROM AUTHOR]